diff --git a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/WfRunForm.tsx b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/WfRunForm.tsx
index b4663c731..9a76c8bb2 100644
--- a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/WfRunForm.tsx
+++ b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/WfRunForm.tsx
@@ -23,21 +23,24 @@ export const WfRunForm = forwardRef<HTMLFormElement, Prop>(({ wfSpecVariables, o
     onSubmit(data)
   }
 
+  // Sort variables so required fields come first
+  const sortedVariables = wfSpecVariables.sort((a, b) => {
+    if (a.required === b.required) return 0
+    return a.required ? -1 : 1
+  })
+
   return (
     <FormProvider {...methods}>
-      <form onSubmit={handleSubmit(onSubmitForm)} ref={ref}>
+      <form onSubmit={handleSubmit(onSubmitForm)} ref={ref} className="space-y-4">
         <div>
-          <Label htmlFor="custom-id">Custom WfRun Id</Label>
-          <Input
-            type="text"
-            className="mb-4 mt-1"
-            id="custom-id"
-            {...register('custom-id-wfRun-flow')}
-            placeholder="Enter string value"
-          />
+          <Label htmlFor="customWfRunId" className="mb-2 flex items-center gap-2">
+            Custom WfRun Id
+            <span className="rounded bg-gray-300 p-1 text-xs">Optional</span>
+          </Label>
+          <Input type="text" id="customWfRunId" {...register('customWfRunId')} placeholder="Enter string value" />
         </div>
-        {!!wfSpecVariables?.length &&
-          wfSpecVariables.map((variable: ThreadVarDef) => (
+        {!!sortedVariables.length &&
+          sortedVariables.map((variable: ThreadVarDef) => (
             <FormFields key={variable.varDef?.name} variables={variable} register={register} formState={formState} />
           ))}
       </form>
diff --git a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/BaseFormField.tsx b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/BaseFormField.tsx
new file mode 100644
index 000000000..9d4a96f28
--- /dev/null
+++ b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/BaseFormField.tsx
@@ -0,0 +1,75 @@
+import { Label } from '@/components/ui/label'
+import { FormFieldProp } from '@/types'
+import { CircleAlert } from 'lucide-react'
+import { FC, ReactNode } from 'react'
+import { useFormContext } from 'react-hook-form'
+import { accessLevels } from '../../../wfSpec/[...props]/components/Variables'
+import { Button } from '@/components/ui/button'
+
+type BaseFormFieldProps = FormFieldProp & {
+  children: ReactNode
+  isDisabled: boolean
+  setIsDisabled: (disabled: boolean) => void
+}
+
+export const BaseFormField: FC<BaseFormFieldProps> = ({
+  variables,
+  formState: { errors },
+  children,
+  isDisabled,
+  setIsDisabled,
+}) => {
+  const { setValue, trigger } = useFormContext()
+
+  if (!variables?.varDef?.name) return null
+
+  const {
+    varDef: { name },
+    required,
+    accessLevel,
+  } = variables
+
+  const handleSetNull = () => {
+    setValue(name, null)
+    trigger(name)
+    setIsDisabled(true)
+  }
+
+  const handleEnable = () => {
+    setIsDisabled(false)
+  }
+
+  return (
+    <div>
+      <div className="mb-2 flex justify-between">
+        <Label htmlFor={name} className="flex items-center gap-2">
+          {name}
+          <span className="rounded bg-green-300 p-1 text-xs">{accessLevels[accessLevel]}</span>
+          {required ? (
+            <span className="rounded bg-red-300 p-1 text-xs">Required</span>
+          ) : (
+            <span className="rounded bg-gray-300 p-1 text-xs">Optional</span>
+          )}
+        </Label>
+        {!required && (
+          <Button
+            type="button"
+            variant="outline"
+            size="sm"
+            onClick={isDisabled ? handleEnable : handleSetNull}
+            className="h-8"
+          >
+            {isDisabled ? 'Enter Value' : 'Set Null'}
+          </Button>
+        )}
+      </div>
+      {children}
+      {errors[name] && (
+        <p className="mt-2 flex items-center gap-1 text-sm text-destructive">
+          <CircleAlert size={16} />
+          {errors[name]?.message}
+        </p>
+      )}
+    </div>
+  )
+}
diff --git a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormInput.tsx b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormInput.tsx
index e2ba9a178..804552b10 100644
--- a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormInput.tsx
+++ b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormInput.tsx
@@ -1,77 +1,49 @@
 import { VARIABLE_TYPES } from '@/app/constants'
 import { Input } from '@/components/ui/input'
-import { Label } from '@/components/ui/label'
+import { cn } from '@/components/utils'
 import { FormFieldProp } from '@/types'
 import { VariableType } from 'littlehorse-client/proto'
-import { CircleAlert } from 'lucide-react'
-import { FC, useState } from 'react'
-import { accessLevels } from '../../../wfSpec/[...props]/components/Variables'
+import { FC, useEffect, useState } from 'react'
+import { useFormContext } from 'react-hook-form'
+import { BaseFormField } from './BaseFormField'
 
 export const FormInput: FC<FormFieldProp> = props => {
-  const [isDisabled, setIsDisabled] = useState(false)
+  const [isDisabled, setIsDisabled] = useState(!props.variables?.required)
+  const { setValue } = useFormContext()
+
+  useEffect(() => {
+    if (!props.variables?.required && props.variables?.varDef?.name) {
+      setValue(props.variables.varDef.name, null)
+    }
+  }, [props.variables, setValue])
+
   if (!props.variables?.varDef?.name) return null
 
   const {
     variables: {
       varDef: { type, name },
       required,
-      accessLevel,
     },
     register,
     formState: { errors },
   } = props
 
-  const variableToType = (variable: VariableType) => {
-    switch (variable) {
-      case VariableType.INT:
-        return 'number'
-      case VariableType.DOUBLE:
-        return 'number'
-      case VariableType.BYTES:
-        return 'number'
-      case VariableType.STR:
-        return 'text'
-      default:
-        return 'text'
-    }
-  }
-
-  const setValue = (value: number | string) => {
-    if (value === null) return value
-    return variableToType(type) === 'number' ? parseFloat(value?.toString()) || undefined : value || undefined
-  }
-
   return (
-    <div>
-      <div className="mb-2 flex justify-between">
-        <Label htmlFor={name} className="flex items-center gap-2">
-          {name}
-          <span className="rounded bg-green-300 p-1 text-xs">{accessLevels[accessLevel]}</span>
-          {required ? (
-            <span className="rounded bg-red-300 p-1 text-xs">Required</span>
-          ) : (
-            <span className="rounded bg-gray-300 p-1 text-xs">Optional</span>
-          )}
-        </Label>
-      </div>
+    <BaseFormField {...props} isDisabled={isDisabled} setIsDisabled={setIsDisabled}>
       <Input
-        type={variableToType(type)}
-        className={errors[name] ? 'mb-1 mt-2 border-red-700' : 'mb-4 mt-1'}
+        type={type === VariableType.INT || type === VariableType.DOUBLE ? 'number' : 'text'}
+        className={cn(errors[name] && 'border-destructive')}
         id={name}
         step={type === VariableType.DOUBLE ? '0.01' : undefined}
         disabled={isDisabled}
         placeholder={`Enter ${VARIABLE_TYPES[type]?.toLowerCase()} value`}
         {...register(name, {
           required: required ? `${name} is required` : false,
-          setValueAs: setValue,
+          setValueAs: (value: string) => {
+            return type === VariableType.INT || type === VariableType.DOUBLE ? parseFloat(value) || undefined : value
+          },
         })}
       />
-      {errors[name] && (
-        <p className="mb-3 flex items-center gap-1 text-sm text-red-700">
-          <CircleAlert size={16} />
-          {errors[name]?.message}
-        </p>
-      )}
-    </div>
+    </BaseFormField>
   )
 }
diff --git a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormSelect.tsx b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormSelect.tsx
index c3ba897fa..daf2d3505 100644
--- a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormSelect.tsx
+++ b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormSelect.tsx
@@ -1,20 +1,19 @@
-import { Label } from '@/components/ui/label'
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select'
 import { FormFieldProp } from '@/types'
-import { CircleAlert } from 'lucide-react'
-import { FC, useState } from 'react'
+import { FC, useEffect, useState } from 'react'
 import { useFormContext } from 'react-hook-form'
-import { accessLevels } from '../../../wfSpec/[...props]/components/Variables'
+import { BaseFormField } from './BaseFormField'
+import { cn } from '@/components/utils'
 
 export const FormSelect: FC<FormFieldProp> = props => {
-  const {
-    register,
-    setValue,
-    formState: { errors },
-    getValues,
-    trigger,
-  } = useFormContext()
-  const [isDisabled, setIsDisabled] = useState(false)
+  const [isDisabled, setIsDisabled] = useState(!props.variables?.required)
+  const { register, setValue, getValues, trigger } = useFormContext()
+
+  useEffect(() => {
+    if (!props.variables?.required && props.variables?.varDef?.name) {
+      setValue(props.variables.varDef.name, null)
+    }
+  }, [props.variables, setValue])
 
   if (!props.variables?.varDef?.name) return null
 
@@ -22,55 +21,33 @@ export const FormSelect: FC<FormFieldProp> = props => {
     variables: {
       varDef: { name },
       required,
-      accessLevel,
     },
   } = props
 
   const handleChange = (value: string) => {
-    if (value === 'none') setValue(name, undefined)
-    else {
-      const booleanValue = value === 'true'
-      setValue(name, booleanValue)
-    }
+    const booleanValue = value === 'true'
+    setValue(name, booleanValue)
     trigger(name)
   }
 
   const value = getValues(name)
 
   return (
-    <div>
-      <div className="mb-2 flex justify-between">
-        <Label htmlFor={name} className="center flex items-center gap-2">
-          {name}
-          <span className="rounded bg-green-300 p-1 text-xs">{accessLevels[accessLevel]}</span>
-          {required ? (
-            <span className="rounded bg-red-300 p-1 text-xs">Required</span>
-          ) : (
-            <span className="rounded bg-gray-300 p-1 text-xs">Optional</span>
-          )}
-        </Label>
-      </div>
+    <BaseFormField {...props} isDisabled={isDisabled} setIsDisabled={setIsDisabled}>
       <Select
         value={value?.toString() || ''}
         onValueChange={handleChange}
         disabled={isDisabled}
         {...register(name, { required: required ? `${name} is required` : false })}
       >
-        <SelectTrigger id={name} className={errors[name] ? 'mb-1 mt-1 border-red-700' : 'mb-4 mt-1'}>
+        <SelectTrigger id={name} className={cn(props.formState.errors[name] && 'border-destructive')}>
           <SelectValue placeholder="Select True or False" />
         </SelectTrigger>
         <SelectContent>
           <SelectItem value="true">True</SelectItem>
           <SelectItem value="false">False</SelectItem>
-          <SelectItem value="none">None</SelectItem>
         </SelectContent>
       </Select>
-      {errors[name]?.message && (
-        <p className="mb-3 flex items-center gap-1 text-sm text-red-700">
-          <CircleAlert size={16} />
-          {String(errors[name]?.message)}
-        </p>
-      )}
-    </div>
+    </BaseFormField>
   )
 }
diff --git a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormTextarea.tsx b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormTextarea.tsx
index adebb0dce..336def7bb 100644
--- a/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormTextarea.tsx
+++ b/dashboard/src/app/(authenticated)/(diagram)/components/Forms/components/FormTextarea.tsx
@@ -1,23 +1,26 @@
-import { Label } from '@/components/ui/label'
+import { VARIABLE_TYPES } from '@/app/constants'
 import { Textarea } from '@/components/ui/textarea'
+import { cn } from '@/components/utils'
 import { FormFieldProp } from '@/types'
-import { FC, useState } from 'react'
-
-import { VARIABLE_TYPES } from '@/app/constants'
-import { CircleAlert } from 'lucide-react'
+import { FC, useEffect, useState } from 'react'
 import { useFormContext } from 'react-hook-form'
-import { accessLevels } from '../../../wfSpec/[...props]/components/Variables'
+import { BaseFormField } from './BaseFormField'
 import { getValidation } from './validation'
 
 export const FormTextarea: FC<FormFieldProp> = props => {
-  const [isDisabled, setIsDisabled] = useState(false)
+  const [isDisabled, setIsDisabled] = useState(!props.variables?.required)
   const { setValue, trigger } = useFormContext()
 
-  if (!props.variables?.varDef?.name) return
+  useEffect(() => {
+    if (!props.variables?.required && props.variables?.varDef?.name) {
+      setValue(props.variables.varDef.name, null)
+    }
+  }, [props.variables, setValue])
+
+  if (!props.variables?.varDef?.name) return null
   const {
     variables: {
       varDef: { type, name },
-      accessLevel,
       required,
     },
     register,
@@ -25,20 +28,9 @@ export const FormTextarea: FC<FormFieldProp> = props => {
   } = props
 
   return (
-    <div>
-      <div className="flex justify-between">
-        <Label htmlFor={name} className="flex items-center gap-2">
-          {name}
-          <span className="rounded bg-green-300 p-1 text-xs">{accessLevels[accessLevel]}</span>
-          {required ? (
-            <span className="rounded bg-red-300 p-1 text-xs">Required</span>
-          ) : (
-            <span className="rounded bg-gray-300 p-1 text-xs">Optional</span>
-          )}
-        </Label>
-      </div>
+    <BaseFormField {...props} isDisabled={isDisabled} setIsDisabled={setIsDisabled}>
       <Textarea
-        className={errors[name] ? 'mb-1 mt-1 min-h-[120px] border-red-700' : 'mb-4 mt-1 rounded-xl'}
+        className={cn(errors[name] && 'border-destructive')}
         id={name}
         disabled={isDisabled}
         placeholder={`Enter ${VARIABLE_TYPES[type]?.toLowerCase()} value`}
@@ -46,18 +38,12 @@ export const FormTextarea: FC<FormFieldProp> = props => {
           required: required ? `${name} is required` : false,
           validate: getValidation(type),
           onChange: e => {
-            setValue(name, e.target.value || undefined)
+            setValue(name, e.target.value)
             trigger(name)
           },
         })}
         defaultValue=""
       />
-      {errors[name] && (
-        <p className="mb-3 flex items-center gap-1 text-sm text-red-700">
-          <CircleAlert size={16} />
-          {errors[name]?.message}
-        </p>
-      )}
-    </div>
+    </BaseFormField>
   )
 }
diff --git a/dashboard/src/app/(authenticated)/(diagram)/components/Modals/ExecuteWorkflowRun.tsx b/dashboard/src/app/(authenticated)/(diagram)/components/Modals/ExecuteWorkflowRun.tsx
index a18a1ebf7..c99705106 100644
--- a/dashboard/src/app/(authenticated)/(diagram)/components/Modals/ExecuteWorkflowRun.tsx
+++ b/dashboard/src/app/(authenticated)/(diagram)/components/Modals/ExecuteWorkflowRun.tsx
@@ -27,6 +27,7 @@ export const ExecuteWorkflowRun: FC<Modal> = ({ data }) => {
 
   const formatVariablesPayload = (values: FormValues) => {
     const transformedObj = Object.keys(values).reduce((acc: Record<string, FormValues>, key) => {
+      if (values[key] === undefined) return acc
       acc[key] = { [matchVariableType(key)]: values[key] }
       return acc
     }, {})
@@ -52,14 +53,16 @@ export const ExecuteWorkflowRun: FC<Modal> = ({ data }) => {
   }
 
   const handleFormSubmit = async (values: FormValues) => {
-    const customWfRunId = values['custom-id-wfRun-flow'] as string
-    delete values['custom-id-wfRun-flow']
+    const customWfRunId = values.customWfRunId as string
+    delete values.customWfRunId
     if (!lhWorkflowSpec.id) return
     try {
       const wfRun = await runWfSpec({
-        ...lhWorkflowSpec.id,
-        wfSpecName: lhWorkflowSpec.id.name,
         tenantId,
+        wfSpecName: lhWorkflowSpec.id.name,
+        majorVersion: lhWorkflowSpec.id.majorVersion,
+        revision: lhWorkflowSpec.id.revision,
+
         id: customWfRunId || undefined,
         variables: formatVariablesPayload(values),
       })
diff --git a/dashboard/src/app/(authenticated)/(diagram)/wfRun/[...ids]/components/Variables.tsx b/dashboard/src/app/(authenticated)/(diagram)/wfRun/[...ids]/components/Variables.tsx
index 7e23cdf1a..e49d4a781 100644
--- a/dashboard/src/app/(authenticated)/(diagram)/wfRun/[...ids]/components/Variables.tsx
+++ b/dashboard/src/app/(authenticated)/(diagram)/wfRun/[...ids]/components/Variables.tsx
@@ -17,6 +17,7 @@ const accessLevels: { [key in WfRunVariableAccessLevel]: string } = {
 
 export const Variables: FC<VariablesProps> = ({ variableDefs, variables }) => {
   if (variableDefs.length === 0) return <></>
+
   return (
     <div className="">
       <h2 className="text-md mb-2 font-bold">Variables</h2>
diff --git a/docs/docs/08-api.md b/docs/docs/08-api.md
index 39502196f..fc79749fa 100644
--- a/docs/docs/08-api.md
+++ b/docs/docs/08-api.md
@@ -468,6 +468,12 @@ languages [here](/docs/developer-guide/grpc), but we put this here for the true
 | ------------ | ------------- | ------------|
 |  [PutPrincipalRequest](#putprincipalrequest)  |  [Principal](#principal)  | EXPERIMENTAL: Creates an Principal. |
 
+### RPC `GetPrincipal` {#getprincipal}
+
+| Request Type | Response Type | Description |
+| ------------ | ------------- | ------------|
+|  [PrincipalId](#principalid)  |  [Principal](#principal)  |  |
+
 ### RPC `Whoami` {#whoami}
 
 | Request Type | Response Type | Description |
@@ -770,6 +776,22 @@ have to worry about this in daily LittleHorse usage.
 | `literal_value` | oneof `source`| [VariableValue](#variablevalue) | Assign a literal value |
 | `format_string` | oneof `source`| [VariableAssignment.FormatString](#variableassignmentformatstring) | Assign a format string |
 | `node_output` | oneof `source`| [VariableAssignment.NodeOutputReference](#variableassignmentnodeoutputreference) | Assign the value of a NodeOutput. |
+| `expression` | oneof `source`| [VariableAssignment.Expression](#variableassignmentexpression) | Assign the value of an Expression. |
+ <!-- end Fields -->
+ <!-- end HasFields -->
+
+
+
+### Message `VariableAssignment.Expression` {#variableassignmentexpression}
+
+An Expression allows you to combine multiple values into one.
+
+
+| Field | Label | Type | Description |
+| ----- | ----  | ---- | ----------- |
+| `lhs` | | [VariableAssignment](#variableassignment) | The left-hand-side of the expression. |
+| `operation` | | [VariableMutationType](#variablemutationtype) | The operator in the expression. |
+| `rhs` | | [VariableAssignment](#variableassignment) | The right-hand-side of the expression. |
  <!-- end Fields -->
  <!-- end HasFields -->
 
diff --git a/lhctl/go.work.sum b/lhctl/go.work.sum
new file mode 100644
index 000000000..960543bf6
--- /dev/null
+++ b/lhctl/go.work.sum
@@ -0,0 +1,15 @@
+cel.dev/expr v0.15.0/go.mod h1:TRSuuV7DlVCE/uwv5QbAiW/v8l5O8C4eEPHeu7gf7Sg=
+github.com/census-instrumentation/opencensus-proto v0.4.1/go.mod h1:4T9NM4+4Vw91VeyqjLS6ao50K5bOcLKN6Q42XnYaRYw=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/cncf/xds/go v0.0.0-20240423153145-555b57ec207b/go.mod h1:W+zGtBO5Y1IgJhy4+A9GOqVhqLpfZi+vwmdNXUehLA8=
+github.com/envoyproxy/go-control-plane v0.12.1-0.20240621013728-1eb8caab5155/go.mod h1:5Wkq+JduFtdAXihLmeTJf+tRYIT4KBc2vPXDhwVo1pA=
+github.com/envoyproxy/protoc-gen-validate v1.0.4/go.mod h1:qys6tmnRsYrQqIhm2bvKZH4Blx/1gTIZ2UKVY1M+Yew=
+github.com/golang/glog v1.2.1/go.mod h1:6AhwSGph0fcJtXVM/PEHPqZlFeoLxhs7/t5UDAwmO+w=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10/go.mod h1:t/avpk3KcrXxUnYOhZhMXJlSEyie6gQbtLq5NM3loB8=
+golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/sync v0.8.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/term v0.23.0/go.mod h1:DgV24QBUrK6jhZXl+20l6UWznPlwAHm1Q1mGHtydmSk=
+golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/genproto/googleapis/api v0.0.0-20240604185151-ef581f913117/go.mod h1:OimBR/bc1wPO9iV4NC2bpyjy3VnAwZh5EBPQdtaE5oo=
diff --git a/lhctl/internal/principal.go b/lhctl/internal/principal.go
index 8cf4da8d9..d767c48c4 100644
--- a/lhctl/internal/principal.go
+++ b/lhctl/internal/principal.go
@@ -48,6 +48,20 @@ var putPrincipalCmd = &cobra.Command{
 	},
 }
 
+var getPrincipalCmd = &cobra.Command{
+	Use:   "principal <id>",
+	Short: "Get a Principal",
+	Args:  cobra.ExactArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		littlehorse.PrintResp(getGlobalClient(cmd).GetPrincipal(
+			requestContext(cmd),
+			&lhproto.PrincipalId{
+				Id: args[0],
+			},
+		))
+	},
+}
+
 var searchPrincipalCmd = &cobra.Command{
 	Use:   "principal",
 	Short: "Search for Principals",
@@ -201,6 +215,8 @@ func init() {
 	searchPrincipalCmd.Flags().Int("earliestMinutesAgo", -1, "Search only for Principals that were created no more than this number of minutes ago")
 	searchPrincipalCmd.Flags().Int("latestMinutesAgo", -1, "Search only for Principals that were created at least this number of minutes ago")
 
+	getCmd.AddCommand(getPrincipalCmd)
+
 	deployCmd.AddCommand(deployPrincipalCmd)
 	deleteCmd.AddCommand(deletePrincipalCmd)
 }
diff --git a/local-dev/issue-certificates.sh b/local-dev/issue-certificates.sh
index 0ba49a1a2..25668f7f3 100755
--- a/local-dev/issue-certificates.sh
+++ b/local-dev/issue-certificates.sh
@@ -51,7 +51,7 @@ echo "Creating Client Certificates"
 openssl req -newkey rsa:2048 -nodes \
     -out "$CLIENT_PATH/client.csr" \
     -keyout "$CLIENT_PATH/client.key" \
-    -subj "/CN=localhost/O=client organization" \
+    -subj "/CN=obiwan/O=client organization" \
     -addext "subjectAltName = DNS:localhost" > /dev/null 2>&1
 openssl x509 -req -sha256 -days 3650 \
     -CA "$CA_PATH/ca.crt" \
diff --git a/schemas/littlehorse/common_wfspec.proto b/schemas/littlehorse/common_wfspec.proto
index 86b03680a..4128e0618 100644
--- a/schemas/littlehorse/common_wfspec.proto
+++ b/schemas/littlehorse/common_wfspec.proto
@@ -39,6 +39,16 @@ message VariableAssignment {
     string node_name = 1;
   }
 
+  // An Expression allows you to combine multiple values into one.
+  message Expression {
+    // The left-hand-side of the expression.
+    VariableAssignment lhs = 1;
+    // The operator in the expression.
+    VariableMutationType operation = 2;
+    // The right-hand-side of the expression.
+    VariableAssignment rhs = 3;
+  }
+
   // If you provide a `variable_name` and the specified variable is JSON_OBJ or
   // JSON_ARR type, then you may also provide a json_path which makes the VariableAssignment
   // resolve to the specified field.
@@ -54,6 +64,8 @@ message VariableAssignment {
     FormatString format_string = 4;
     // Assign the value of a NodeOutput.
     NodeOutputReference node_output = 5;
+    // Assign the value of an Expression.
+    Expression expression = 6;
   }
 }
 
diff --git a/schemas/littlehorse/service.proto b/schemas/littlehorse/service.proto
index b93070b82..f3ad42b06 100644
--- a/schemas/littlehorse/service.proto
+++ b/schemas/littlehorse/service.proto
@@ -285,6 +285,8 @@ service LittleHorse {
   // EXPERIMENTAL: Creates an Principal.
   rpc PutPrincipal(PutPrincipalRequest) returns (Principal) {}
 
+  rpc GetPrincipal(PrincipalId) returns (Principal) {}
+
   // Returns the Principal of the caller.
   rpc Whoami(google.protobuf.Empty) returns (Principal) {}
 
diff --git a/sdk-dotnet/LittleHorse.Sdk.Tests/LHLoggerFactoryProviderTest.cs b/sdk-dotnet/LittleHorse.Sdk.Tests/LHLoggerFactoryProviderTest.cs
deleted file mode 100644
index e3d79ed78..000000000
--- a/sdk-dotnet/LittleHorse.Sdk.Tests/LHLoggerFactoryProviderTest.cs
+++ /dev/null
@@ -1,40 +0,0 @@
-using System;
-using Microsoft.Extensions.Logging;
-using Moq;
-using Xunit;
-
-namespace LittleHorse.Sdk.Tests.Internal
-{
-    public class LHLoggerFactoryProviderTest
-    {
-        [Fact]
-        public void Initialize_WithCustomLoggerFactory_ShouldCreateLogger()
-        {
-            var mockLoggerFactory = new Mock<ILoggerFactory>();
-            
-            LHLoggerFactoryProvider.Initialize(mockLoggerFactory.Object);
-            var logger = LHLoggerFactoryProvider.GetLogger<string>();
-            
-            Assert.NotNull(logger);
-            Assert.IsAssignableFrom<ILogger<string>>(logger);
-        }
-        
-        [Fact]
-        public void Initialize_WithoutLoggerFactory_ShouldAVoidWritingLogs()
-        {
-            LHLoggerFactoryProvider.Initialize();
-            var logger = LHLoggerFactoryProvider.GetLogger<string>();
-            logger.LogInformation("This log should not be printed.");
-            
-            Assert.NotNull(logger);
-        }
-        
-        [Fact]
-        public void GetLogger_WithoutInitialize_ShouldThrowInvalidOperationException()
-        {
-            var exception = Assert.Throws<InvalidOperationException>(() => LHLoggerFactoryProvider.GetLogger<string>());
-            
-            Assert.Equal("_loggerFactory does not have a valid value and it is trying to create a logger instance.", exception.Message);
-        }
-    }
-}
diff --git a/sdk-dotnet/LittleHorse.Sdk.Tests/LHTaskSignatureTest.cs b/sdk-dotnet/LittleHorse.Sdk.Tests/LHTaskSignatureTest.cs
index ad7137284..2fc89b565 100644
--- a/sdk-dotnet/LittleHorse.Sdk.Tests/LHTaskSignatureTest.cs
+++ b/sdk-dotnet/LittleHorse.Sdk.Tests/LHTaskSignatureTest.cs
@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using LittleHorse.Common.Proto;
+using LittleHorse.Sdk;
 using LittleHorse.Sdk.Exceptions;
 using LittleHorse.Sdk.Worker;
 using LittleHorse.Sdk.Worker.Internal;
@@ -20,6 +21,11 @@ public class LHTaskSignatureTest
     const string DETAIL_ATTR_NAME = "detail";
     const string TELEPHONE_ATTR_NAME = "telephone";
     
+    public LHTaskSignatureTest()
+    {
+        LHLoggerFactoryProvider.Initialize(null);
+    }
+    
     [Fact]
     public void TaskSignature_WithLHTaskMethodAndLHTypeAttributes_ShouldBuildLHSignatureWithInputAndOutput()
     {
diff --git a/sdk-dotnet/LittleHorse.Sdk.Tests/TestClasses.cs b/sdk-dotnet/LittleHorse.Sdk.Tests/TestClasses.cs
index 6ec3afe4e..c5510365f 100644
--- a/sdk-dotnet/LittleHorse.Sdk.Tests/TestClasses.cs
+++ b/sdk-dotnet/LittleHorse.Sdk.Tests/TestClasses.cs
@@ -10,7 +10,7 @@ public class Car
 
 public class Person
 {
-    public string FirstName { get; set; }
+    public string? FirstName { get; set; }
     public int Age { get; set; }
-    public List<Car> Cars { get; set; }
+    public List<Car>? Cars { get; set; }
 }
\ No newline at end of file
diff --git a/sdk-dotnet/LittleHorse.Sdk.Tests/Utils/JsonHandlerTest.cs b/sdk-dotnet/LittleHorse.Sdk.Tests/Utils/JsonHandlerTest.cs
index 436a71f0a..a9370eb26 100644
--- a/sdk-dotnet/LittleHorse.Sdk.Tests/Utils/JsonHandlerTest.cs
+++ b/sdk-dotnet/LittleHorse.Sdk.Tests/Utils/JsonHandlerTest.cs
@@ -26,11 +26,11 @@ public void JsonHandler_WithJsonString_ShouldReturnCustomObject()
             
             var result = JsonHandler.DeserializeFromJson(jsonString, typeof(Person));
             
-            var actual = (Person) result;
+            var actual = (Person) result!;
             
             Assert.Equal("Test", actual.FirstName);
             Assert.Equal(35, actual.Age);
-            Assert.Equal(1, actual.Cars[0].Id);
+            Assert.Equal(1, actual.Cars![0].Id);
             Assert.Equal(134.45E-2f, actual.Cars[0].Cost);
         }
     }
diff --git a/sdk-dotnet/LittleHorse.Sdk.Tests/Worker/VariableMappingTest.cs b/sdk-dotnet/LittleHorse.Sdk.Tests/Worker/VariableMappingTest.cs
new file mode 100644
index 000000000..0e664e5f4
--- /dev/null
+++ b/sdk-dotnet/LittleHorse.Sdk.Tests/Worker/VariableMappingTest.cs
@@ -0,0 +1,336 @@
+using System;
+using System.Collections.Generic;
+using Google.Protobuf;
+using Type = System.Type;
+using LittleHorse.Common.Proto;
+using LittleHorse.Sdk.Exceptions;
+using LittleHorse.Sdk.Helper;
+using LittleHorse.Sdk.Worker;
+using Moq;
+using Newtonsoft.Json;
+using Xunit;
+
+namespace LittleHorse.Sdk.Tests.Worker;
+
+public class VariableMappingTest
+{
+    public VariableMappingTest()
+    {
+        LHLoggerFactoryProvider.Initialize(null);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithValidLHTypes_ShouldBeBuiltSuccessfully()
+    {
+        int position = 0;
+        string paramName = "param_test";
+        
+        var testAllowedTypes = new List<Type>() 
+        {
+            typeof(Int64), typeof(Int32), typeof(Int16) 
+            , typeof(UInt16), typeof(UInt32), typeof(UInt64)
+            , typeof(sbyte), typeof(byte), typeof(short), typeof(ushort)
+            , typeof(int), typeof(uint), typeof(long) 
+            , typeof(ulong), typeof(nint), typeof(nuint), typeof(float), typeof(double)
+            , typeof(String), typeof(bool), typeof(byte[]), typeof(List<string>)
+            , typeof(List<object>), typeof(List<string>), typeof(List<int>)
+        };
+
+        foreach (var type in testAllowedTypes)
+        {
+            var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type);
+            TaskDef taskDef = getTaskDefForTest(variableType);
+        
+            var result = new VariableMapping(taskDef, position, type, paramName);
+        
+            Assert.True(result is not null);   
+        }
+    }
+
+    [Fact]
+    public void VariableMapping_WithMismatchTypesInt_ShouldThrowException()
+    {
+        Type type1 = typeof(Int64);
+        Type type2 = typeof(string);
+        var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type1);
+        TaskDef taskDef = getTaskDefForTest(variableType);
+        
+        var exception = Assert.Throws<LHTaskSchemaMismatchException>(
+            () => new VariableMapping(taskDef, 0, type2, "any param name"));
+            
+        Assert.Contains($"TaskDef provides INT, func accepts", exception.Message);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithMismatchTypeDouble_ShouldThrowException()
+    {
+        Type type1 = typeof(double);
+        Type type2 = typeof(Int64);
+        var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type1);
+        TaskDef taskDef = getTaskDefForTest(variableType);
+        
+        var exception = Assert.Throws<LHTaskSchemaMismatchException>(
+            () => new VariableMapping(taskDef, 0, type2, "any param name"));
+            
+        Assert.Contains($"TaskDef provides DOUBLE, func accepts", exception.Message);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithMismatchTypeString_ShouldThrowException()
+    {
+        Type type1 = typeof(string);
+        Type type2 = typeof(double);
+        var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type1);
+        TaskDef taskDef = getTaskDefForTest(variableType);
+        
+        var exception = Assert.Throws<LHTaskSchemaMismatchException>(
+            () => new VariableMapping(taskDef, 0, type2, "any param name"));
+            
+        Assert.Contains($"TaskDef provides STRING, func accepts", exception.Message);
+    }
+
+    [Fact]
+    public void VariableMapping_WithMismatchTypeBool_ShouldThrowException()
+    {
+        Type type1 = typeof(bool);
+        Type type2 = typeof(string);
+        var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type1);
+        TaskDef taskDef = getTaskDefForTest(variableType);
+        
+        var exception = Assert.Throws<LHTaskSchemaMismatchException>(
+            () => new VariableMapping(taskDef, 0, type2, "any param name"));
+            
+        Assert.Contains($"TaskDef provides BOOL, func accepts", exception.Message);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithMismatchTypeBytes_ShouldThrowException()
+    {
+        Type type1 = typeof(byte[]);
+        Type type2 = typeof(string);
+        var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type1);
+        TaskDef taskDef = getTaskDefForTest(variableType);
+        
+        var exception = Assert.Throws<LHTaskSchemaMismatchException>(
+            () => new VariableMapping(taskDef, 0, type2, "any param name"));
+            
+        Assert.Contains($"TaskDef provides BYTES, func accepts", exception.Message);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignIntValue_ShouldReturnInt32Object()
+    {
+        int expectedValue = 29;
+        var testAllowedTypes = new List<Type>() { typeof(Int32), typeof(Int16) 
+            , typeof(UInt16), typeof(UInt32)
+            , typeof(sbyte), typeof(byte), typeof(short), typeof(ushort)
+            , typeof(int), typeof(uint)
+            , typeof(nint), typeof(nuint)};
+        
+        int position = 0;
+        string paramName = "param_test";
+
+        foreach (var type in testAllowedTypes)
+        {
+            var variableMapping = getVariableMappingForTest(type, paramName, position);
+            VariableValue variableValue = new VariableValue {Int = expectedValue};
+            ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+            var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+            var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+            Assert.Equal((int) taskInstance.Variables[0].Value.Int, result);
+        }
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignLongValue_ShouldReturnInt64Object()
+    {
+        int expectedValue = 29;
+        var testAllowedTypes = new List<Type>() { typeof(Int64), typeof(UInt64), typeof(long), typeof(ulong)};
+        
+        int position = 0;
+        string paramName = "param_test";
+
+        foreach (var type in testAllowedTypes)
+        {
+            var variableMapping = getVariableMappingForTest(type, paramName, position);
+            VariableValue variableValue = new VariableValue {Int = expectedValue};
+            ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+            var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+            var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+            Assert.Equal(taskInstance.Variables[0].Value.Int, result);
+        }
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignDoubleValue_ShouldReturnDoubleObject()
+    {
+        float expectedValue = 3_000.5F;
+        var testAllowedTypes = new List<Type>() { typeof(double), typeof(Double)};
+        
+        int position = 0;
+        string paramName = "param_test";
+
+        foreach (var type in testAllowedTypes)
+        {
+            var variableMapping = getVariableMappingForTest(type, paramName, position);
+            VariableValue variableValue = new VariableValue {Double = expectedValue};
+            ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+            var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+            var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+            Assert.Equal(taskInstance.Variables[0].Value.Double, result);
+        }
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignDoubleValue_ShouldReturnFloatObject()
+    {
+        float expectedValue = 3_000.5F;
+        var type = typeof(float);
+        
+        int position = 0;
+        string paramName = "param_test";
+        
+        var variableMapping = getVariableMappingForTest(type, paramName, position);
+        VariableValue variableValue = new VariableValue {Double = expectedValue};
+        ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+        var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+    
+        var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+    
+        Assert.Equal((float) taskInstance.Variables[0].Value.Double, result);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignStringValue_ShouldReturnStrObject()
+    {
+        Type type = typeof(string);
+        int position = 0;
+        string paramName = "param_test";
+        var variableMapping = getVariableMappingForTest(type, paramName, position);
+        VariableValue variableValue = new VariableValue { Str = "param_value_test"};
+        ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+        var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+        var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+        Assert.Equal(taskInstance.Variables[0].Value.Str, result);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignBytesValue_ShouldReturnBytesObject()
+    {
+        byte[] expectedValue = new byte[] { 0x20, 0x20, 0x20 };
+        ByteString byteString = ByteString.CopyFrom(expectedValue);
+        Type type = typeof(byte[]);
+        int position = 0;
+        string paramName = "param_test";
+        var variableMapping = getVariableMappingForTest(type, paramName, position);
+        VariableValue variableValue = new VariableValue { Bytes = byteString};
+        ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+        var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+        var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+        Assert.Equal(taskInstance.Variables[0].Value.Bytes, result);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignBoolValue_ShouldReturnBoolObject()
+    {
+        bool expectedValue = false;
+        Type type = typeof(bool);
+        int position = 0;
+        string paramName = "param_test";
+        var variableMapping = getVariableMappingForTest(type, paramName, position);
+        VariableValue variableValue = new VariableValue { Bool = expectedValue};
+        ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+        var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+        var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+        Assert.Equal(taskInstance.Variables[0].Value.Bool, result);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignArrayObjectValue_ShouldReturnArrayObject()
+    {
+        string value = "[{\"FirstName\":\"Test\",\"Age\":35,\"Cars\":[{\"Id\":1,\"Cost\":1.3445}]}]";
+        Type type = typeof(List<Person>);
+        int position = 0;
+        string paramName = "param_test";
+        var variableMapping = getVariableMappingForTest(type, paramName, position);
+        VariableValue variableValue = new VariableValue { JsonArr = value};
+        ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+        var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+        var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+        var expectedList = (List<Person>)JsonConvert.DeserializeObject(value, type)!;
+        var actualList = (List<Person>)result!;
+        
+        Assert.Equal(expectedList.Count, actualList.Count);
+        Assert.Equal(expectedList[0].FirstName, actualList[0].FirstName);
+        Assert.Equal(expectedList[0].Age, actualList[0].Age);
+        Assert.Equal(expectedList[0].Cars!.Count, actualList[0].Cars!.Count);
+    }
+    
+    [Fact]
+    public void VariableMapping_WithAssignJsonStringValue_ShouldReturnCustomObject()
+    {
+        string value = "{\"FirstName\":\"Test\",\"Age\":35,\"Cars\":[{\"Id\":1,\"Cost\":1.3445}]}";
+        Type type = typeof(Person);
+        int position = 0;
+        string paramName = "param_test";
+        var variableMapping = getVariableMappingForTest(type, paramName, position);
+        VariableValue variableValue = new VariableValue { JsonObj = value};
+        ScheduledTask taskInstance = getScheduledTaskForTest(variableValue, paramName);
+        var mockWorkerContext = new Mock<LHWorkerContext>(taskInstance, new DateTime());
+        
+        var result = variableMapping.Assign(taskInstance, mockWorkerContext.Object);
+        
+        var expectedObject = (Person)JsonConvert.DeserializeObject(value, type)!;
+        var actualObject = (Person)result!;
+        
+        Assert.Equal(expectedObject.FirstName, actualObject.FirstName);
+        Assert.Equal(expectedObject.Age, actualObject.Age);
+        Assert.Equal(expectedObject.Cars!.Count, actualObject.Cars!.Count);
+    }
+
+    private TaskDef getTaskDefForTest(VariableType type)
+    {
+        var inputVar = new VariableDef();
+        inputVar.Type = type;
+        TaskDef taskDef = new TaskDef();
+        TaskDefId taskDefId = new TaskDefId();
+        taskDef.Id = taskDefId;
+        taskDef.InputVars.Add(inputVar);
+        
+        return taskDef;
+    }
+
+    private VariableMapping getVariableMappingForTest(Type type, string paramName, int position)
+    {
+        var variableType = LHMappingHelper.MapDotNetTypeToLHVariableType(type);
+        TaskDef taskDef = getTaskDefForTest(variableType);
+        
+        var variableMapping = new VariableMapping(taskDef, position, type, paramName);
+        
+        return variableMapping;
+    }
+
+    private ScheduledTask getScheduledTaskForTest(VariableValue variableValue, string variableName)
+    {
+        ScheduledTask scheduledTask = new ScheduledTask();
+        List<VarNameAndVal> variables = new List<VarNameAndVal>();
+        variables.Add(new VarNameAndVal {VarName = variableName, Value = variableValue, Masked = true});
+        scheduledTask.Variables.Add(variables);
+
+        return scheduledTask;
+    }
+}
\ No newline at end of file
diff --git a/sdk-dotnet/LittleHorse.Sdk/Helper/LHMappingHelper.cs b/sdk-dotnet/LittleHorse.Sdk/Helper/LHMappingHelper.cs
index 192709545..118be46cf 100644
--- a/sdk-dotnet/LittleHorse.Sdk/Helper/LHMappingHelper.cs
+++ b/sdk-dotnet/LittleHorse.Sdk/Helper/LHMappingHelper.cs
@@ -203,5 +203,13 @@ private static Double GetFloatingValue(object obj)
                 _ => throw new LHInputVarSubstitutionException("Object value can not be converted to a Double.")
             };
         }
+
+        public static bool isInt64Type(Type type)
+        {
+            return type.IsAssignableFrom(typeof(Int64))
+                   || type.IsAssignableFrom(typeof(UInt64))
+                   || type.IsAssignableFrom(typeof(long))
+                   || type.IsAssignableFrom(typeof(ulong));
+        }
     }
 }
diff --git a/sdk-dotnet/LittleHorse.Sdk/Worker/LHTaskSignature.cs b/sdk-dotnet/LittleHorse.Sdk/Worker/LHTaskSignature.cs
index 8807042ac..ba3ead229 100644
--- a/sdk-dotnet/LittleHorse.Sdk/Worker/LHTaskSignature.cs
+++ b/sdk-dotnet/LittleHorse.Sdk/Worker/LHTaskSignature.cs
@@ -24,7 +24,7 @@ public class LHTaskSignature<T>
 
         public LHTaskSignature(string taskDefName, T executable)
         {
-            _logger = new LoggerFactory().CreateLogger<LHTaskSignature<T>>();
+            _logger = LHLoggerFactoryProvider.GetLogger<LHTaskSignature<T>>();
             _lhMethodParams = new List<LHMethodParam>();
             TaskDefName = taskDefName;
             Executable = executable;
diff --git a/sdk-dotnet/LittleHorse.Sdk/Worker/VariableMapping.cs b/sdk-dotnet/LittleHorse.Sdk/Worker/VariableMapping.cs
index a557fe683..36514461b 100644
--- a/sdk-dotnet/LittleHorse.Sdk/Worker/VariableMapping.cs
+++ b/sdk-dotnet/LittleHorse.Sdk/Worker/VariableMapping.cs
@@ -8,7 +8,7 @@ namespace LittleHorse.Sdk.Worker
 {
     public class VariableMapping
     {
-        private ILogger? _logger;
+        private ILogger<VariableMapping>? _logger;
         private string? _name;
         private Type _type;
         private int _position;
@@ -45,19 +45,19 @@ public VariableMapping(TaskDef taskDef, int position, Type type, string? paramNa
             switch (val.ValueCase)
             {
                 case VariableValue.ValueOneofCase.Int:
-                    if (_type == typeof(long) || _type == typeof(long?))
+                    if (LHMappingHelper.isInt64Type(_type))
                     {
                         return val.Int;
                     }
 
-                    return (int)val.Int;
+                    return (int) val.Int;
                 case VariableValue.ValueOneofCase.Double:
-                    if (_type == typeof(double) || _type == typeof(double?))
+                    if (_type == typeof(double) || _type == typeof(Double))
                     {
                         return val.Double;
                     }
 
-                    return (float)val.Double;
+                    return (float) val.Double;
                 case VariableValue.ValueOneofCase.Str:
                     return val.Str;
                 case VariableValue.ValueOneofCase.Bytes:
diff --git a/sdk-go/lhproto/common_wfspec.pb.go b/sdk-go/lhproto/common_wfspec.pb.go
index 64052a00d..d21722fb4 100644
--- a/sdk-go/lhproto/common_wfspec.pb.go
+++ b/sdk-go/lhproto/common_wfspec.pb.go
@@ -255,6 +255,7 @@ type VariableAssignment struct {
 	//	*VariableAssignment_LiteralValue
 	//	*VariableAssignment_FormatString_
 	//	*VariableAssignment_NodeOutput
+	//	*VariableAssignment_Expression_
 	Source isVariableAssignment_Source `protobuf_oneof:"source"`
 }
 
@@ -332,6 +333,13 @@ func (x *VariableAssignment) GetNodeOutput() *VariableAssignment_NodeOutputRefer
 	return nil
 }
 
+func (x *VariableAssignment) GetExpression() *VariableAssignment_Expression {
+	if x, ok := x.GetSource().(*VariableAssignment_Expression_); ok {
+		return x.Expression
+	}
+	return nil
+}
+
 type isVariableAssignment_Source interface {
 	isVariableAssignment_Source()
 }
@@ -356,6 +364,11 @@ type VariableAssignment_NodeOutput struct {
 	NodeOutput *VariableAssignment_NodeOutputReference `protobuf:"bytes,5,opt,name=node_output,json=nodeOutput,proto3,oneof"`
 }
 
+type VariableAssignment_Expression_ struct {
+	// Assign the value of an Expression.
+	Expression *VariableAssignment_Expression `protobuf:"bytes,6,opt,name=expression,proto3,oneof"`
+}
+
 func (*VariableAssignment_VariableName) isVariableAssignment_Source() {}
 
 func (*VariableAssignment_LiteralValue) isVariableAssignment_Source() {}
@@ -364,6 +377,8 @@ func (*VariableAssignment_FormatString_) isVariableAssignment_Source() {}
 
 func (*VariableAssignment_NodeOutput) isVariableAssignment_Source() {}
 
+func (*VariableAssignment_Expression_) isVariableAssignment_Source() {}
+
 // A VariableMutation defines a modification made to one of a ThreadRun's variables.
 // The LHS determines the variable that is modified; the operation determines how
 // it is modified, and the RHS is the input to the operation.
@@ -1016,6 +1031,73 @@ func (x *VariableAssignment_NodeOutputReference) GetNodeName() string {
 	return ""
 }
 
+// An Expression allows you to combine multiple values into one.
+type VariableAssignment_Expression struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The left-hand-side of the expression.
+	Lhs *VariableAssignment `protobuf:"bytes,1,opt,name=lhs,proto3" json:"lhs,omitempty"`
+	// The operator in the expression.
+	Operation VariableMutationType `protobuf:"varint,2,opt,name=operation,proto3,enum=littlehorse.VariableMutationType" json:"operation,omitempty"`
+	// The right-hand-side of the expression.
+	Rhs *VariableAssignment `protobuf:"bytes,3,opt,name=rhs,proto3" json:"rhs,omitempty"`
+}
+
+func (x *VariableAssignment_Expression) Reset() {
+	*x = VariableAssignment_Expression{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_common_wfspec_proto_msgTypes[8]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *VariableAssignment_Expression) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*VariableAssignment_Expression) ProtoMessage() {}
+
+func (x *VariableAssignment_Expression) ProtoReflect() protoreflect.Message {
+	mi := &file_common_wfspec_proto_msgTypes[8]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use VariableAssignment_Expression.ProtoReflect.Descriptor instead.
+func (*VariableAssignment_Expression) Descriptor() ([]byte, []int) {
+	return file_common_wfspec_proto_rawDescGZIP(), []int{0, 2}
+}
+
+func (x *VariableAssignment_Expression) GetLhs() *VariableAssignment {
+	if x != nil {
+		return x.Lhs
+	}
+	return nil
+}
+
+func (x *VariableAssignment_Expression) GetOperation() VariableMutationType {
+	if x != nil {
+		return x.Operation
+	}
+	return VariableMutationType_ASSIGN
+}
+
+func (x *VariableAssignment_Expression) GetRhs() *VariableAssignment {
+	if x != nil {
+		return x.Rhs
+	}
+	return nil
+}
+
 // Specifies to use the output of a NodeRun as the RHS.
 type VariableMutation_NodeOutputSource struct {
 	state         protoimpl.MessageState
@@ -1029,7 +1111,7 @@ type VariableMutation_NodeOutputSource struct {
 func (x *VariableMutation_NodeOutputSource) Reset() {
 	*x = VariableMutation_NodeOutputSource{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_common_wfspec_proto_msgTypes[8]
+		mi := &file_common_wfspec_proto_msgTypes[9]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1042,7 +1124,7 @@ func (x *VariableMutation_NodeOutputSource) String() string {
 func (*VariableMutation_NodeOutputSource) ProtoMessage() {}
 
 func (x *VariableMutation_NodeOutputSource) ProtoReflect() protoreflect.Message {
-	mi := &file_common_wfspec_proto_msgTypes[8]
+	mi := &file_common_wfspec_proto_msgTypes[9]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1075,7 +1157,7 @@ type UTActionTrigger_UTACancel struct {
 func (x *UTActionTrigger_UTACancel) Reset() {
 	*x = UTActionTrigger_UTACancel{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_common_wfspec_proto_msgTypes[9]
+		mi := &file_common_wfspec_proto_msgTypes[10]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1088,7 +1170,7 @@ func (x *UTActionTrigger_UTACancel) String() string {
 func (*UTActionTrigger_UTACancel) ProtoMessage() {}
 
 func (x *UTActionTrigger_UTACancel) ProtoReflect() protoreflect.Message {
-	mi := &file_common_wfspec_proto_msgTypes[9]
+	mi := &file_common_wfspec_proto_msgTypes[10]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1119,7 +1201,7 @@ type UTActionTrigger_UTATask struct {
 func (x *UTActionTrigger_UTATask) Reset() {
 	*x = UTActionTrigger_UTATask{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_common_wfspec_proto_msgTypes[10]
+		mi := &file_common_wfspec_proto_msgTypes[11]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1132,7 +1214,7 @@ func (x *UTActionTrigger_UTATask) String() string {
 func (*UTActionTrigger_UTATask) ProtoMessage() {}
 
 func (x *UTActionTrigger_UTATask) ProtoReflect() protoreflect.Message {
-	mi := &file_common_wfspec_proto_msgTypes[10]
+	mi := &file_common_wfspec_proto_msgTypes[11]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1179,7 +1261,7 @@ type UTActionTrigger_UTAReassign struct {
 func (x *UTActionTrigger_UTAReassign) Reset() {
 	*x = UTActionTrigger_UTAReassign{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_common_wfspec_proto_msgTypes[11]
+		mi := &file_common_wfspec_proto_msgTypes[12]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1192,7 +1274,7 @@ func (x *UTActionTrigger_UTAReassign) String() string {
 func (*UTActionTrigger_UTAReassign) ProtoMessage() {}
 
 func (x *UTActionTrigger_UTAReassign) ProtoReflect() protoreflect.Message {
-	mi := &file_common_wfspec_proto_msgTypes[11]
+	mi := &file_common_wfspec_proto_msgTypes[12]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1230,7 +1312,7 @@ var file_common_wfspec_proto_rawDesc = []byte{
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+	0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x45, 0x78, 0x70, 0x6f,
+	0x6e, 0x65, 0x6e, 0x74, 0x69, 0x61, 0x6c, 0x42, 0x61, 0x63, 0x6b, 0x6f, 0x66, 0x66, 0x52, 0x65,
+	0x74, 0x72, 0x79, 0x50, 0x6f, 0x6c, 0x69, 0x63, 0x79, 0x48, 0x01, 0x52, 0x12, 0x65, 0x78, 0x70,
+	0x6f, 0x6e, 0x65, 0x6e, 0x74, 0x69, 0x61, 0x6c, 0x42, 0x61, 0x63, 0x6b, 0x6f, 0x66, 0x66, 0x88,
+	0x01, 0x01, 0x12, 0x3d, 0x0a, 0x09, 0x76, 0x61, 0x72, 0x69, 0x61, 0x62, 0x6c, 0x65, 0x73, 0x18,
+	0x04, 0x20, 0x03, 0x28, 0x0b, 0x32, 0x1f, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f,
+	0x72, 0x73, 0x65, 0x2e, 0x56, 0x61, 0x72, 0x69, 0x61, 0x62, 0x6c, 0x65, 0x41, 0x73, 0x73, 0x69,
+	0x67, 0x6e, 0x6d, 0x65, 0x6e, 0x74, 0x52, 0x09, 0x76, 0x61, 0x72, 0x69, 0x61, 0x62, 0x6c, 0x65,
+	0x73, 0x42, 0x11, 0x0a, 0x0f, 0x74, 0x61, 0x73, 0x6b, 0x5f, 0x74, 0x6f, 0x5f, 0x65, 0x78, 0x65,
+	0x63, 0x75, 0x74, 0x65, 0x42, 0x16, 0x0a, 0x14, 0x5f, 0x65, 0x78, 0x70, 0x6f, 0x6e, 0x65, 0x6e,
+	0x74, 0x69, 0x61, 0x6c, 0x5f, 0x62, 0x61, 0x63, 0x6b, 0x6f, 0x66, 0x66, 0x2a, 0x98, 0x01, 0x0a,
+	0x14, 0x56, 0x61, 0x72, 0x69, 0x61, 0x62, 0x6c, 0x65, 0x4d, 0x75, 0x74, 0x61, 0x74, 0x69, 0x6f,
+	0x6e, 0x54, 0x79, 0x70, 0x65, 0x12, 0x0a, 0x0a, 0x06, 0x41, 0x53, 0x53, 0x49, 0x47, 0x4e, 0x10,
+	0x00, 0x12, 0x07, 0x0a, 0x03, 0x41, 0x44, 0x44, 0x10, 0x01, 0x12, 0x0a, 0x0a, 0x06, 0x45, 0x58,
+	0x54, 0x45, 0x4e, 0x44, 0x10, 0x02, 0x12, 0x0c, 0x0a, 0x08, 0x53, 0x55, 0x42, 0x54, 0x52, 0x41,
+	0x43, 0x54, 0x10, 0x03, 0x12, 0x0c, 0x0a, 0x08, 0x4d, 0x55, 0x4c, 0x54, 0x49, 0x50, 0x4c, 0x59,
+	0x10, 0x04, 0x12, 0x0a, 0x0a, 0x06, 0x44, 0x49, 0x56, 0x49, 0x44, 0x45, 0x10, 0x05, 0x12, 0x15,
+	0x0a, 0x11, 0x52, 0x45, 0x4d, 0x4f, 0x56, 0x45, 0x5f, 0x49, 0x46, 0x5f, 0x50, 0x52, 0x45, 0x53,
+	0x45, 0x4e, 0x54, 0x10, 0x06, 0x12, 0x10, 0x0a, 0x0c, 0x52, 0x45, 0x4d, 0x4f, 0x56, 0x45, 0x5f,
+	0x49, 0x4e, 0x44, 0x45, 0x58, 0x10, 0x07, 0x12, 0x0e, 0x0a, 0x0a, 0x52, 0x45, 0x4d, 0x4f, 0x56,
+	0x45, 0x5f, 0x4b, 0x45, 0x59, 0x10, 0x08, 0x2a, 0x84, 0x01, 0x0a, 0x0a, 0x43, 0x6f, 0x6d, 0x70,
+	0x61, 0x72, 0x61, 0x74, 0x6f, 0x72, 0x12, 0x0d, 0x0a, 0x09, 0x4c, 0x45, 0x53, 0x53, 0x5f, 0x54,
+	0x48, 0x41, 0x4e, 0x10, 0x00, 0x12, 0x10, 0x0a, 0x0c, 0x47, 0x52, 0x45, 0x41, 0x54, 0x45, 0x52,
+	0x5f, 0x54, 0x48, 0x41, 0x4e, 0x10, 0x01, 0x12, 0x10, 0x0a, 0x0c, 0x4c, 0x45, 0x53, 0x53, 0x5f,
+	0x54, 0x48, 0x41, 0x4e, 0x5f, 0x45, 0x51, 0x10, 0x02, 0x12, 0x13, 0x0a, 0x0f, 0x47, 0x52, 0x45,
+	0x41, 0x54, 0x45, 0x52, 0x5f, 0x54, 0x48, 0x41, 0x4e, 0x5f, 0x45, 0x51, 0x10, 0x03, 0x12, 0x0a,
+	0x0a, 0x06, 0x45, 0x51, 0x55, 0x41, 0x4c, 0x53, 0x10, 0x04, 0x12, 0x0e, 0x0a, 0x0a, 0x4e, 0x4f,
+	0x54, 0x5f, 0x45, 0x51, 0x55, 0x41, 0x4c, 0x53, 0x10, 0x05, 0x12, 0x06, 0x0a, 0x02, 0x49, 0x4e,
+	0x10, 0x06, 0x12, 0x0a, 0x0a, 0x06, 0x4e, 0x4f, 0x54, 0x5f, 0x49, 0x4e, 0x10, 0x07, 0x42, 0x49,
+	0x0a, 0x1f, 0x69, 0x6f, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65,
+	0x2e, 0x73, 0x64, 0x6b, 0x2e, 0x63, 0x6f, 0x6d, 0x6d, 0x6f, 0x6e, 0x2e, 0x70, 0x72, 0x6f, 0x74,
+	0x6f, 0x50, 0x01, 0x5a, 0x09, 0x2e, 0x3b, 0x6c, 0x68, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0xaa, 0x02,
+	0x18, 0x4c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x48, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x43, 0x6f, 0x6d,
+	0x6d, 0x6f, 0x6e, 0x2e, 0x50, 0x72, 0x6f, 0x74, 0x6f, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f,
+	0x33,
 }
 
 var (
@@ -1424,7 +1523,7 @@ func file_common_wfspec_proto_rawDescGZIP() []byte {
 }
 
 var file_common_wfspec_proto_enumTypes = make([]protoimpl.EnumInfo, 3)
-var file_common_wfspec_proto_msgTypes = make([]protoimpl.MessageInfo, 12)
+var file_common_wfspec_proto_msgTypes = make([]protoimpl.MessageInfo, 13)
 var file_common_wfspec_proto_goTypes = []interface{}{
 	(VariableMutationType)(0),                      // 0: littlehorse.VariableMutationType
 	(Comparator)(0),                                // 1: littlehorse.Comparator
@@ -1437,44 +1536,49 @@ var file_common_wfspec_proto_goTypes = []interface{}{
 	(*TaskNode)(nil),                               // 8: littlehorse.TaskNode
 	(*VariableAssignment_FormatString)(nil),        // 9: littlehorse.VariableAssignment.FormatString
 	(*VariableAssignment_NodeOutputReference)(nil), // 10: littlehorse.VariableAssignment.NodeOutputReference
-	(*VariableMutation_NodeOutputSource)(nil),      // 11: littlehorse.VariableMutation.NodeOutputSource
-	(*UTActionTrigger_UTACancel)(nil),              // 12: littlehorse.UTActionTrigger.UTACancel
-	(*UTActionTrigger_UTATask)(nil),                // 13: littlehorse.UTActionTrigger.UTATask
-	(*UTActionTrigger_UTAReassign)(nil),            // 14: littlehorse.UTActionTrigger.UTAReassign
-	(*VariableValue)(nil),                          // 15: littlehorse.VariableValue
-	(VariableType)(0),                              // 16: littlehorse.VariableType
-	(*TaskDefId)(nil),                              // 17: littlehorse.TaskDefId
+	(*VariableAssignment_Expression)(nil),          // 11: littlehorse.VariableAssignment.Expression
+	(*VariableMutation_NodeOutputSource)(nil),      // 12: littlehorse.VariableMutation.NodeOutputSource
+	(*UTActionTrigger_UTACancel)(nil),              // 13: littlehorse.UTActionTrigger.UTACancel
+	(*UTActionTrigger_UTATask)(nil),                // 14: littlehorse.UTActionTrigger.UTATask
+	(*UTActionTrigger_UTAReassign)(nil),            // 15: littlehorse.UTActionTrigger.UTAReassign
+	(*VariableValue)(nil),                          // 16: littlehorse.VariableValue
+	(VariableType)(0),                              // 17: littlehorse.VariableType
+	(*TaskDefId)(nil),                              // 18: littlehorse.TaskDefId
 }
 var file_common_wfspec_proto_depIdxs = []int32{
-	15, // 0: littlehorse.VariableAssignment.literal_value:type_name -> littlehorse.VariableValue
+	16, // 0: littlehorse.VariableAssignment.literal_value:type_name -> littlehorse.VariableValue
 	9,  // 1: littlehorse.VariableAssignment.format_string:type_name -> littlehorse.VariableAssignment.FormatString
 	10, // 2: littlehorse.VariableAssignment.node_output:type_name -> littlehorse.VariableAssignment.NodeOutputReference
-	0,  // 3: littlehorse.VariableMutation.operation:type_name -> littlehorse.VariableMutationType
-	3,  // 4: littlehorse.VariableMutation.source_variable:type_name -> littlehorse.VariableAssignment
-	15, // 5: littlehorse.VariableMutation.literal_value:type_name -> littlehorse.VariableValue
-	11, // 6: littlehorse.VariableMutation.node_output:type_name -> littlehorse.VariableMutation.NodeOutputSource
-	16, // 7: littlehorse.VariableDef.type:type_name -> littlehorse.VariableType
-	15, // 8: littlehorse.VariableDef.default_value:type_name -> littlehorse.VariableValue
-	13, // 9: littlehorse.UTActionTrigger.task:type_name -> littlehorse.UTActionTrigger.UTATask
-	12, // 10: littlehorse.UTActionTrigger.cancel:type_name -> littlehorse.UTActionTrigger.UTACancel
-	14, // 11: littlehorse.UTActionTrigger.reassign:type_name -> littlehorse.UTActionTrigger.UTAReassign
-	3,  // 12: littlehorse.UTActionTrigger.delay_seconds:type_name -> littlehorse.VariableAssignment
-	2,  // 13: littlehorse.UTActionTrigger.hook:type_name -> littlehorse.UTActionTrigger.UTHook
-	17, // 14: littlehorse.TaskNode.task_def_id:type_name -> littlehorse.TaskDefId
-	3,  // 15: littlehorse.TaskNode.dynamic_task:type_name -> littlehorse.VariableAssignment
-	7,  // 16: littlehorse.TaskNode.exponential_backoff:type_name -> littlehorse.ExponentialBackoffRetryPolicy
-	3,  // 17: littlehorse.TaskNode.variables:type_name -> littlehorse.VariableAssignment
-	3,  // 18: littlehorse.VariableAssignment.FormatString.format:type_name -> littlehorse.VariableAssignment
-	3,  // 19: littlehorse.VariableAssignment.FormatString.args:type_name -> littlehorse.VariableAssignment
-	8,  // 20: littlehorse.UTActionTrigger.UTATask.task:type_name -> littlehorse.TaskNode
-	4,  // 21: littlehorse.UTActionTrigger.UTATask.mutations:type_name -> littlehorse.VariableMutation
-	3,  // 22: littlehorse.UTActionTrigger.UTAReassign.user_id:type_name -> littlehorse.VariableAssignment
-	3,  // 23: littlehorse.UTActionTrigger.UTAReassign.user_group:type_name -> littlehorse.VariableAssignment
-	24, // [24:24] is the sub-list for method output_type
-	24, // [24:24] is the sub-list for method input_type
-	24, // [24:24] is the sub-list for extension type_name
-	24, // [24:24] is the sub-list for extension extendee
-	0,  // [0:24] is the sub-list for field type_name
+	11, // 3: littlehorse.VariableAssignment.expression:type_name -> littlehorse.VariableAssignment.Expression
+	0,  // 4: littlehorse.VariableMutation.operation:type_name -> littlehorse.VariableMutationType
+	3,  // 5: littlehorse.VariableMutation.source_variable:type_name -> littlehorse.VariableAssignment
+	16, // 6: littlehorse.VariableMutation.literal_value:type_name -> littlehorse.VariableValue
+	12, // 7: littlehorse.VariableMutation.node_output:type_name -> littlehorse.VariableMutation.NodeOutputSource
+	17, // 8: littlehorse.VariableDef.type:type_name -> littlehorse.VariableType
+	16, // 9: littlehorse.VariableDef.default_value:type_name -> littlehorse.VariableValue
+	14, // 10: littlehorse.UTActionTrigger.task:type_name -> littlehorse.UTActionTrigger.UTATask
+	13, // 11: littlehorse.UTActionTrigger.cancel:type_name -> littlehorse.UTActionTrigger.UTACancel
+	15, // 12: littlehorse.UTActionTrigger.reassign:type_name -> littlehorse.UTActionTrigger.UTAReassign
+	3,  // 13: littlehorse.UTActionTrigger.delay_seconds:type_name -> littlehorse.VariableAssignment
+	2,  // 14: littlehorse.UTActionTrigger.hook:type_name -> littlehorse.UTActionTrigger.UTHook
+	18, // 15: littlehorse.TaskNode.task_def_id:type_name -> littlehorse.TaskDefId
+	3,  // 16: littlehorse.TaskNode.dynamic_task:type_name -> littlehorse.VariableAssignment
+	7,  // 17: littlehorse.TaskNode.exponential_backoff:type_name -> littlehorse.ExponentialBackoffRetryPolicy
+	3,  // 18: littlehorse.TaskNode.variables:type_name -> littlehorse.VariableAssignment
+	3,  // 19: littlehorse.VariableAssignment.FormatString.format:type_name -> littlehorse.VariableAssignment
+	3,  // 20: littlehorse.VariableAssignment.FormatString.args:type_name -> littlehorse.VariableAssignment
+	3,  // 21: littlehorse.VariableAssignment.Expression.lhs:type_name -> littlehorse.VariableAssignment
+	0,  // 22: littlehorse.VariableAssignment.Expression.operation:type_name -> littlehorse.VariableMutationType
+	3,  // 23: littlehorse.VariableAssignment.Expression.rhs:type_name -> littlehorse.VariableAssignment
+	8,  // 24: littlehorse.UTActionTrigger.UTATask.task:type_name -> littlehorse.TaskNode
+	4,  // 25: littlehorse.UTActionTrigger.UTATask.mutations:type_name -> littlehorse.VariableMutation
+	3,  // 26: littlehorse.UTActionTrigger.UTAReassign.user_id:type_name -> littlehorse.VariableAssignment
+	3,  // 27: littlehorse.UTActionTrigger.UTAReassign.user_group:type_name -> littlehorse.VariableAssignment
+	28, // [28:28] is the sub-list for method output_type
+	28, // [28:28] is the sub-list for method input_type
+	28, // [28:28] is the sub-list for extension type_name
+	28, // [28:28] is the sub-list for extension extendee
+	0,  // [0:28] is the sub-list for field type_name
 }
 
 func init() { file_common_wfspec_proto_init() }
@@ -1583,7 +1687,7 @@ func file_common_wfspec_proto_init() {
 			}
 		}
 		file_common_wfspec_proto_msgTypes[8].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*VariableMutation_NodeOutputSource); i {
+			switch v := v.(*VariableAssignment_Expression); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -1595,7 +1699,7 @@ func file_common_wfspec_proto_init() {
 			}
 		}
 		file_common_wfspec_proto_msgTypes[9].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*UTActionTrigger_UTACancel); i {
+			switch v := v.(*VariableMutation_NodeOutputSource); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -1607,7 +1711,7 @@ func file_common_wfspec_proto_init() {
 			}
 		}
 		file_common_wfspec_proto_msgTypes[10].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*UTActionTrigger_UTATask); i {
+			switch v := v.(*UTActionTrigger_UTACancel); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -1619,6 +1723,18 @@ func file_common_wfspec_proto_init() {
 			}
 		}
 		file_common_wfspec_proto_msgTypes[11].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*UTActionTrigger_UTATask); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_common_wfspec_proto_msgTypes[12].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*UTActionTrigger_UTAReassign); i {
 			case 0:
 				return &v.state
@@ -1636,6 +1752,7 @@ func file_common_wfspec_proto_init() {
 		(*VariableAssignment_LiteralValue)(nil),
 		(*VariableAssignment_FormatString_)(nil),
 		(*VariableAssignment_NodeOutput)(nil),
+		(*VariableAssignment_Expression_)(nil),
 	}
 	file_common_wfspec_proto_msgTypes[1].OneofWrappers = []interface{}{
 		(*VariableMutation_SourceVariable)(nil),
@@ -1652,15 +1769,15 @@ func file_common_wfspec_proto_init() {
 		(*TaskNode_TaskDefId)(nil),
 		(*TaskNode_DynamicTask)(nil),
 	}
-	file_common_wfspec_proto_msgTypes[8].OneofWrappers = []interface{}{}
-	file_common_wfspec_proto_msgTypes[11].OneofWrappers = []interface{}{}
+	file_common_wfspec_proto_msgTypes[9].OneofWrappers = []interface{}{}
+	file_common_wfspec_proto_msgTypes[12].OneofWrappers = []interface{}{}
 	type x struct{}
 	out := protoimpl.TypeBuilder{
 		File: protoimpl.DescBuilder{
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_common_wfspec_proto_rawDesc,
 			NumEnums:      3,
-			NumMessages:   12,
+			NumMessages:   13,
 			NumExtensions: 0,
 			NumServices:   0,
 		},
diff --git a/sdk-go/lhproto/service.pb.go b/sdk-go/lhproto/service.pb.go
index 0d1f1a77c..21892823a 100644
--- a/sdk-go/lhproto/service.pb.go
+++ b/sdk-go/lhproto/service.pb.go
@@ -7110,7 +7110,7 @@ var file_service_proto_rawDesc = []byte{
 	0x4c, 0x5f, 0x55, 0x50, 0x44, 0x41, 0x54, 0x45, 0x53, 0x10, 0x00, 0x12, 0x1a, 0x0a, 0x16, 0x4d,
 	0x49, 0x4e, 0x4f, 0x52, 0x5f, 0x52, 0x45, 0x56, 0x49, 0x53, 0x49, 0x4f, 0x4e, 0x5f, 0x55, 0x50,
 	0x44, 0x41, 0x54, 0x45, 0x53, 0x10, 0x01, 0x12, 0x0e, 0x0a, 0x0a, 0x4e, 0x4f, 0x5f, 0x55, 0x50,
-	0x44, 0x41, 0x54, 0x45, 0x53, 0x10, 0x02, 0x32, 0xea, 0x2f, 0x0a, 0x0b, 0x4c, 0x69, 0x74, 0x74,
+	0x44, 0x41, 0x54, 0x45, 0x53, 0x10, 0x02, 0x32, 0xae, 0x30, 0x0a, 0x0b, 0x4c, 0x69, 0x74, 0x74,
 	0x6c, 0x65, 0x48, 0x6f, 0x72, 0x73, 0x65, 0x12, 0x44, 0x0a, 0x0a, 0x50, 0x75, 0x74, 0x54, 0x61,
 	0x73, 0x6b, 0x44, 0x65, 0x66, 0x12, 0x1e, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f,
 	0x72, 0x73, 0x65, 0x2e, 0x50, 0x75, 0x74, 0x54, 0x61, 0x73, 0x6b, 0x44, 0x65, 0x66, 0x52, 0x65,
@@ -7484,21 +7484,25 @@ var file_service_proto_rawDesc = []byte{
 	0x61, 0x6c, 0x12, 0x20, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65,
 	0x2e, 0x50, 0x75, 0x74, 0x50, 0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x52, 0x65, 0x71,
 	0x75, 0x65, 0x73, 0x74, 0x1a, 0x16, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72,
-	0x73, 0x65, 0x2e, 0x50, 0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x22, 0x00, 0x12, 0x3a,
-	0x0a, 0x06, 0x57, 0x68, 0x6f, 0x61, 0x6d, 0x69, 0x12, 0x16, 0x2e, 0x67, 0x6f, 0x6f, 0x67, 0x6c,
-	0x65, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x62, 0x75, 0x66, 0x2e, 0x45, 0x6d, 0x70, 0x74, 0x79,
-	0x1a, 0x16, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x50,
-	0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x22, 0x00, 0x12, 0x48, 0x0a, 0x10, 0x47, 0x65,
-	0x74, 0x53, 0x65, 0x72, 0x76, 0x65, 0x72, 0x56, 0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e, 0x12, 0x16,
-	0x2e, 0x67, 0x6f, 0x6f, 0x67, 0x6c, 0x65, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x62, 0x75, 0x66,
-	0x2e, 0x45, 0x6d, 0x70, 0x74, 0x79, 0x1a, 0x1a, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68,
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-	0x6f, 0x6e, 0x22, 0x00, 0x42, 0x49, 0x0a, 0x1f, 0x69, 0x6f, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c,
-	0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x73, 0x64, 0x6b, 0x2e, 0x63, 0x6f, 0x6d, 0x6d, 0x6f,
-	0x6e, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x50, 0x01, 0x5a, 0x09, 0x2e, 0x3b, 0x6c, 0x68, 0x70,
-	0x72, 0x6f, 0x74, 0x6f, 0xaa, 0x02, 0x18, 0x4c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x48, 0x6f, 0x72,
-	0x73, 0x65, 0x2e, 0x43, 0x6f, 0x6d, 0x6d, 0x6f, 0x6e, 0x2e, 0x50, 0x72, 0x6f, 0x74, 0x6f, 0x62,
-	0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+	0x73, 0x65, 0x2e, 0x50, 0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x22, 0x00, 0x12, 0x42,
+	0x0a, 0x0c, 0x47, 0x65, 0x74, 0x50, 0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x12, 0x18,
+	0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x50, 0x72, 0x69,
+	0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x49, 0x64, 0x1a, 0x16, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c,
+	0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x50, 0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c,
+	0x22, 0x00, 0x12, 0x3a, 0x0a, 0x06, 0x57, 0x68, 0x6f, 0x61, 0x6d, 0x69, 0x12, 0x16, 0x2e, 0x67,
+	0x6f, 0x6f, 0x67, 0x6c, 0x65, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x62, 0x75, 0x66, 0x2e, 0x45,
+	0x6d, 0x70, 0x74, 0x79, 0x1a, 0x16, 0x2e, 0x6c, 0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72,
+	0x73, 0x65, 0x2e, 0x50, 0x72, 0x69, 0x6e, 0x63, 0x69, 0x70, 0x61, 0x6c, 0x22, 0x00, 0x12, 0x48,
+	0x0a, 0x10, 0x47, 0x65, 0x74, 0x53, 0x65, 0x72, 0x76, 0x65, 0x72, 0x56, 0x65, 0x72, 0x73, 0x69,
+	0x6f, 0x6e, 0x12, 0x16, 0x2e, 0x67, 0x6f, 0x6f, 0x67, 0x6c, 0x65, 0x2e, 0x70, 0x72, 0x6f, 0x74,
+	0x6f, 0x62, 0x75, 0x66, 0x2e, 0x45, 0x6d, 0x70, 0x74, 0x79, 0x1a, 0x1a, 0x2e, 0x6c, 0x69, 0x74,
+	0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x53, 0x65, 0x72, 0x76, 0x65, 0x72, 0x56,
+	0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e, 0x22, 0x00, 0x42, 0x49, 0x0a, 0x1f, 0x69, 0x6f, 0x2e, 0x6c,
+	0x69, 0x74, 0x74, 0x6c, 0x65, 0x68, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x73, 0x64, 0x6b, 0x2e, 0x63,
+	0x6f, 0x6d, 0x6d, 0x6f, 0x6e, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x50, 0x01, 0x5a, 0x09, 0x2e,
+	0x3b, 0x6c, 0x68, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0xaa, 0x02, 0x18, 0x4c, 0x69, 0x74, 0x74, 0x6c,
+	0x65, 0x48, 0x6f, 0x72, 0x73, 0x65, 0x2e, 0x43, 0x6f, 0x6d, 0x6d, 0x6f, 0x6e, 0x2e, 0x50, 0x72,
+	0x6f, 0x74, 0x6f, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -7867,84 +7871,86 @@ var file_service_proto_depIdxs = []int32{
 	137, // 197: littlehorse.LittleHorse.PutTenant:input_type -> littlehorse.PutTenantRequest
 	116, // 198: littlehorse.LittleHorse.GetTenant:input_type -> littlehorse.TenantId
 	138, // 199: littlehorse.LittleHorse.PutPrincipal:input_type -> littlehorse.PutPrincipalRequest
-	139, // 200: littlehorse.LittleHorse.Whoami:input_type -> google.protobuf.Empty
-	139, // 201: littlehorse.LittleHorse.GetServerVersion:input_type -> google.protobuf.Empty
-	140, // 202: littlehorse.LittleHorse.PutTaskDef:output_type -> littlehorse.TaskDef
-	140, // 203: littlehorse.LittleHorse.GetTaskDef:output_type -> littlehorse.TaskDef
-	81,  // 204: littlehorse.LittleHorse.GetTaskWorkerGroup:output_type -> littlehorse.TaskWorkerGroup
-	141, // 205: littlehorse.LittleHorse.PutExternalEventDef:output_type -> littlehorse.ExternalEventDef
-	141, // 206: littlehorse.LittleHorse.GetExternalEventDef:output_type -> littlehorse.ExternalEventDef
-	142, // 207: littlehorse.LittleHorse.PutWorkflowEventDef:output_type -> littlehorse.WorkflowEventDef
-	143, // 208: littlehorse.LittleHorse.PutWfSpec:output_type -> littlehorse.WfSpec
-	143, // 209: littlehorse.LittleHorse.GetWfSpec:output_type -> littlehorse.WfSpec
-	143, // 210: littlehorse.LittleHorse.GetLatestWfSpec:output_type -> littlehorse.WfSpec
-	143, // 211: littlehorse.LittleHorse.MigrateWfSpec:output_type -> littlehorse.WfSpec
-	144, // 212: littlehorse.LittleHorse.PutUserTaskDef:output_type -> littlehorse.UserTaskDef
-	144, // 213: littlehorse.LittleHorse.GetUserTaskDef:output_type -> littlehorse.UserTaskDef
-	144, // 214: littlehorse.LittleHorse.GetLatestUserTaskDef:output_type -> littlehorse.UserTaskDef
-	145, // 215: littlehorse.LittleHorse.RunWf:output_type -> littlehorse.WfRun
-	146, // 216: littlehorse.LittleHorse.ScheduleWf:output_type -> littlehorse.ScheduledWfRun
-	78,  // 217: littlehorse.LittleHorse.SearchScheduledWfRun:output_type -> littlehorse.ScheduledWfRunIdList
-	146, // 218: littlehorse.LittleHorse.GetScheduledWfRun:output_type -> littlehorse.ScheduledWfRun
-	145, // 219: littlehorse.LittleHorse.GetWfRun:output_type -> littlehorse.WfRun
-	127, // 220: littlehorse.LittleHorse.GetUserTaskRun:output_type -> littlehorse.UserTaskRun
-	139, // 221: littlehorse.LittleHorse.AssignUserTaskRun:output_type -> google.protobuf.Empty
-	139, // 222: littlehorse.LittleHorse.CompleteUserTaskRun:output_type -> google.protobuf.Empty
-	139, // 223: littlehorse.LittleHorse.CancelUserTaskRun:output_type -> google.protobuf.Empty
-	127, // 224: littlehorse.LittleHorse.SaveUserTaskRunProgress:output_type -> littlehorse.UserTaskRun
-	77,  // 225: littlehorse.LittleHorse.ListUserTaskRuns:output_type -> littlehorse.UserTaskRunList
-	118, // 226: littlehorse.LittleHorse.GetNodeRun:output_type -> littlehorse.NodeRun
-	50,  // 227: littlehorse.LittleHorse.ListNodeRuns:output_type -> littlehorse.NodeRunList
-	129, // 228: littlehorse.LittleHorse.GetTaskRun:output_type -> littlehorse.TaskRun
-	83,  // 229: littlehorse.LittleHorse.ListTaskRuns:output_type -> littlehorse.TaskRunList
-	119, // 230: littlehorse.LittleHorse.GetVariable:output_type -> littlehorse.Variable
-	52,  // 231: littlehorse.LittleHorse.ListVariables:output_type -> littlehorse.VariableList
-	120, // 232: littlehorse.LittleHorse.PutExternalEvent:output_type -> littlehorse.ExternalEvent
-	120, // 233: littlehorse.LittleHorse.GetExternalEvent:output_type -> littlehorse.ExternalEvent
-	121, // 234: littlehorse.LittleHorse.AwaitWorkflowEvent:output_type -> littlehorse.WorkflowEvent
-	142, // 235: littlehorse.LittleHorse.GetWorkflowEventDef:output_type -> littlehorse.WorkflowEventDef
-	121, // 236: littlehorse.LittleHorse.GetWorkflowEvent:output_type -> littlehorse.WorkflowEvent
-	54,  // 237: littlehorse.LittleHorse.ListExternalEvents:output_type -> littlehorse.ExternalEventList
-	56,  // 238: littlehorse.LittleHorse.ListWorkflowEvents:output_type -> littlehorse.WorkflowEventList
-	22,  // 239: littlehorse.LittleHorse.SearchWfRun:output_type -> littlehorse.WfRunIdList
-	26,  // 240: littlehorse.LittleHorse.SearchNodeRun:output_type -> littlehorse.NodeRunIdList
-	24,  // 241: littlehorse.LittleHorse.SearchTaskRun:output_type -> littlehorse.TaskRunIdList
-	28,  // 242: littlehorse.LittleHorse.SearchUserTaskRun:output_type -> littlehorse.UserTaskRunIdList
-	30,  // 243: littlehorse.LittleHorse.SearchVariable:output_type -> littlehorse.VariableIdList
-	46,  // 244: littlehorse.LittleHorse.SearchExternalEvent:output_type -> littlehorse.ExternalEventIdList
-	48,  // 245: littlehorse.LittleHorse.SearchWorkflowEvent:output_type -> littlehorse.WorkflowEventIdList
-	32,  // 246: littlehorse.LittleHorse.SearchTaskDef:output_type -> littlehorse.TaskDefIdList
-	34,  // 247: littlehorse.LittleHorse.SearchUserTaskDef:output_type -> littlehorse.UserTaskDefIdList
-	36,  // 248: littlehorse.LittleHorse.SearchWfSpec:output_type -> littlehorse.WfSpecIdList
-	38,  // 249: littlehorse.LittleHorse.SearchExternalEventDef:output_type -> littlehorse.ExternalEventDefIdList
-	40,  // 250: littlehorse.LittleHorse.SearchWorkflowEventDef:output_type -> littlehorse.WorkflowEventDefIdList
-	42,  // 251: littlehorse.LittleHorse.SearchTenant:output_type -> littlehorse.TenantIdList
-	44,  // 252: littlehorse.LittleHorse.SearchPrincipal:output_type -> littlehorse.PrincipalIdList
-	59,  // 253: littlehorse.LittleHorse.RegisterTaskWorker:output_type -> littlehorse.RegisterTaskWorkerResponse
-	63,  // 254: littlehorse.LittleHorse.PollTask:output_type -> littlehorse.PollTaskResponse
-	139, // 255: littlehorse.LittleHorse.ReportTask:output_type -> google.protobuf.Empty
-	139, // 256: littlehorse.LittleHorse.StopWfRun:output_type -> google.protobuf.Empty
-	139, // 257: littlehorse.LittleHorse.ResumeWfRun:output_type -> google.protobuf.Empty
-	145, // 258: littlehorse.LittleHorse.RescueThreadRun:output_type -> littlehorse.WfRun
-	139, // 259: littlehorse.LittleHorse.DeleteWfRun:output_type -> google.protobuf.Empty
-	139, // 260: littlehorse.LittleHorse.DeleteTaskDef:output_type -> google.protobuf.Empty
-	139, // 261: littlehorse.LittleHorse.DeleteWfSpec:output_type -> google.protobuf.Empty
-	139, // 262: littlehorse.LittleHorse.DeleteUserTaskDef:output_type -> google.protobuf.Empty
-	139, // 263: littlehorse.LittleHorse.DeleteExternalEventDef:output_type -> google.protobuf.Empty
-	139, // 264: littlehorse.LittleHorse.DeleteWorkflowEventDef:output_type -> google.protobuf.Empty
-	139, // 265: littlehorse.LittleHorse.DeletePrincipal:output_type -> google.protobuf.Empty
-	139, // 266: littlehorse.LittleHorse.DeleteScheduledWfRun:output_type -> google.protobuf.Empty
-	74,  // 267: littlehorse.LittleHorse.GetTaskDefMetricsWindow:output_type -> littlehorse.TaskDefMetrics
-	75,  // 268: littlehorse.LittleHorse.GetWfSpecMetricsWindow:output_type -> littlehorse.WfSpecMetrics
-	70,  // 269: littlehorse.LittleHorse.ListTaskDefMetrics:output_type -> littlehorse.ListTaskMetricsResponse
-	73,  // 270: littlehorse.LittleHorse.ListWfSpecMetrics:output_type -> littlehorse.ListWfMetricsResponse
-	147, // 271: littlehorse.LittleHorse.PutTenant:output_type -> littlehorse.Tenant
-	147, // 272: littlehorse.LittleHorse.GetTenant:output_type -> littlehorse.Tenant
-	148, // 273: littlehorse.LittleHorse.PutPrincipal:output_type -> littlehorse.Principal
-	148, // 274: littlehorse.LittleHorse.Whoami:output_type -> littlehorse.Principal
-	86,  // 275: littlehorse.LittleHorse.GetServerVersion:output_type -> littlehorse.ServerVersion
-	202, // [202:276] is the sub-list for method output_type
-	128, // [128:202] is the sub-list for method input_type
+	117, // 200: littlehorse.LittleHorse.GetPrincipal:input_type -> littlehorse.PrincipalId
+	139, // 201: littlehorse.LittleHorse.Whoami:input_type -> google.protobuf.Empty
+	139, // 202: littlehorse.LittleHorse.GetServerVersion:input_type -> google.protobuf.Empty
+	140, // 203: littlehorse.LittleHorse.PutTaskDef:output_type -> littlehorse.TaskDef
+	140, // 204: littlehorse.LittleHorse.GetTaskDef:output_type -> littlehorse.TaskDef
+	81,  // 205: littlehorse.LittleHorse.GetTaskWorkerGroup:output_type -> littlehorse.TaskWorkerGroup
+	141, // 206: littlehorse.LittleHorse.PutExternalEventDef:output_type -> littlehorse.ExternalEventDef
+	141, // 207: littlehorse.LittleHorse.GetExternalEventDef:output_type -> littlehorse.ExternalEventDef
+	142, // 208: littlehorse.LittleHorse.PutWorkflowEventDef:output_type -> littlehorse.WorkflowEventDef
+	143, // 209: littlehorse.LittleHorse.PutWfSpec:output_type -> littlehorse.WfSpec
+	143, // 210: littlehorse.LittleHorse.GetWfSpec:output_type -> littlehorse.WfSpec
+	143, // 211: littlehorse.LittleHorse.GetLatestWfSpec:output_type -> littlehorse.WfSpec
+	143, // 212: littlehorse.LittleHorse.MigrateWfSpec:output_type -> littlehorse.WfSpec
+	144, // 213: littlehorse.LittleHorse.PutUserTaskDef:output_type -> littlehorse.UserTaskDef
+	144, // 214: littlehorse.LittleHorse.GetUserTaskDef:output_type -> littlehorse.UserTaskDef
+	144, // 215: littlehorse.LittleHorse.GetLatestUserTaskDef:output_type -> littlehorse.UserTaskDef
+	145, // 216: littlehorse.LittleHorse.RunWf:output_type -> littlehorse.WfRun
+	146, // 217: littlehorse.LittleHorse.ScheduleWf:output_type -> littlehorse.ScheduledWfRun
+	78,  // 218: littlehorse.LittleHorse.SearchScheduledWfRun:output_type -> littlehorse.ScheduledWfRunIdList
+	146, // 219: littlehorse.LittleHorse.GetScheduledWfRun:output_type -> littlehorse.ScheduledWfRun
+	145, // 220: littlehorse.LittleHorse.GetWfRun:output_type -> littlehorse.WfRun
+	127, // 221: littlehorse.LittleHorse.GetUserTaskRun:output_type -> littlehorse.UserTaskRun
+	139, // 222: littlehorse.LittleHorse.AssignUserTaskRun:output_type -> google.protobuf.Empty
+	139, // 223: littlehorse.LittleHorse.CompleteUserTaskRun:output_type -> google.protobuf.Empty
+	139, // 224: littlehorse.LittleHorse.CancelUserTaskRun:output_type -> google.protobuf.Empty
+	127, // 225: littlehorse.LittleHorse.SaveUserTaskRunProgress:output_type -> littlehorse.UserTaskRun
+	77,  // 226: littlehorse.LittleHorse.ListUserTaskRuns:output_type -> littlehorse.UserTaskRunList
+	118, // 227: littlehorse.LittleHorse.GetNodeRun:output_type -> littlehorse.NodeRun
+	50,  // 228: littlehorse.LittleHorse.ListNodeRuns:output_type -> littlehorse.NodeRunList
+	129, // 229: littlehorse.LittleHorse.GetTaskRun:output_type -> littlehorse.TaskRun
+	83,  // 230: littlehorse.LittleHorse.ListTaskRuns:output_type -> littlehorse.TaskRunList
+	119, // 231: littlehorse.LittleHorse.GetVariable:output_type -> littlehorse.Variable
+	52,  // 232: littlehorse.LittleHorse.ListVariables:output_type -> littlehorse.VariableList
+	120, // 233: littlehorse.LittleHorse.PutExternalEvent:output_type -> littlehorse.ExternalEvent
+	120, // 234: littlehorse.LittleHorse.GetExternalEvent:output_type -> littlehorse.ExternalEvent
+	121, // 235: littlehorse.LittleHorse.AwaitWorkflowEvent:output_type -> littlehorse.WorkflowEvent
+	142, // 236: littlehorse.LittleHorse.GetWorkflowEventDef:output_type -> littlehorse.WorkflowEventDef
+	121, // 237: littlehorse.LittleHorse.GetWorkflowEvent:output_type -> littlehorse.WorkflowEvent
+	54,  // 238: littlehorse.LittleHorse.ListExternalEvents:output_type -> littlehorse.ExternalEventList
+	56,  // 239: littlehorse.LittleHorse.ListWorkflowEvents:output_type -> littlehorse.WorkflowEventList
+	22,  // 240: littlehorse.LittleHorse.SearchWfRun:output_type -> littlehorse.WfRunIdList
+	26,  // 241: littlehorse.LittleHorse.SearchNodeRun:output_type -> littlehorse.NodeRunIdList
+	24,  // 242: littlehorse.LittleHorse.SearchTaskRun:output_type -> littlehorse.TaskRunIdList
+	28,  // 243: littlehorse.LittleHorse.SearchUserTaskRun:output_type -> littlehorse.UserTaskRunIdList
+	30,  // 244: littlehorse.LittleHorse.SearchVariable:output_type -> littlehorse.VariableIdList
+	46,  // 245: littlehorse.LittleHorse.SearchExternalEvent:output_type -> littlehorse.ExternalEventIdList
+	48,  // 246: littlehorse.LittleHorse.SearchWorkflowEvent:output_type -> littlehorse.WorkflowEventIdList
+	32,  // 247: littlehorse.LittleHorse.SearchTaskDef:output_type -> littlehorse.TaskDefIdList
+	34,  // 248: littlehorse.LittleHorse.SearchUserTaskDef:output_type -> littlehorse.UserTaskDefIdList
+	36,  // 249: littlehorse.LittleHorse.SearchWfSpec:output_type -> littlehorse.WfSpecIdList
+	38,  // 250: littlehorse.LittleHorse.SearchExternalEventDef:output_type -> littlehorse.ExternalEventDefIdList
+	40,  // 251: littlehorse.LittleHorse.SearchWorkflowEventDef:output_type -> littlehorse.WorkflowEventDefIdList
+	42,  // 252: littlehorse.LittleHorse.SearchTenant:output_type -> littlehorse.TenantIdList
+	44,  // 253: littlehorse.LittleHorse.SearchPrincipal:output_type -> littlehorse.PrincipalIdList
+	59,  // 254: littlehorse.LittleHorse.RegisterTaskWorker:output_type -> littlehorse.RegisterTaskWorkerResponse
+	63,  // 255: littlehorse.LittleHorse.PollTask:output_type -> littlehorse.PollTaskResponse
+	139, // 256: littlehorse.LittleHorse.ReportTask:output_type -> google.protobuf.Empty
+	139, // 257: littlehorse.LittleHorse.StopWfRun:output_type -> google.protobuf.Empty
+	139, // 258: littlehorse.LittleHorse.ResumeWfRun:output_type -> google.protobuf.Empty
+	145, // 259: littlehorse.LittleHorse.RescueThreadRun:output_type -> littlehorse.WfRun
+	139, // 260: littlehorse.LittleHorse.DeleteWfRun:output_type -> google.protobuf.Empty
+	139, // 261: littlehorse.LittleHorse.DeleteTaskDef:output_type -> google.protobuf.Empty
+	139, // 262: littlehorse.LittleHorse.DeleteWfSpec:output_type -> google.protobuf.Empty
+	139, // 263: littlehorse.LittleHorse.DeleteUserTaskDef:output_type -> google.protobuf.Empty
+	139, // 264: littlehorse.LittleHorse.DeleteExternalEventDef:output_type -> google.protobuf.Empty
+	139, // 265: littlehorse.LittleHorse.DeleteWorkflowEventDef:output_type -> google.protobuf.Empty
+	139, // 266: littlehorse.LittleHorse.DeletePrincipal:output_type -> google.protobuf.Empty
+	139, // 267: littlehorse.LittleHorse.DeleteScheduledWfRun:output_type -> google.protobuf.Empty
+	74,  // 268: littlehorse.LittleHorse.GetTaskDefMetricsWindow:output_type -> littlehorse.TaskDefMetrics
+	75,  // 269: littlehorse.LittleHorse.GetWfSpecMetricsWindow:output_type -> littlehorse.WfSpecMetrics
+	70,  // 270: littlehorse.LittleHorse.ListTaskDefMetrics:output_type -> littlehorse.ListTaskMetricsResponse
+	73,  // 271: littlehorse.LittleHorse.ListWfSpecMetrics:output_type -> littlehorse.ListWfMetricsResponse
+	147, // 272: littlehorse.LittleHorse.PutTenant:output_type -> littlehorse.Tenant
+	147, // 273: littlehorse.LittleHorse.GetTenant:output_type -> littlehorse.Tenant
+	148, // 274: littlehorse.LittleHorse.PutPrincipal:output_type -> littlehorse.Principal
+	148, // 275: littlehorse.LittleHorse.GetPrincipal:output_type -> littlehorse.Principal
+	148, // 276: littlehorse.LittleHorse.Whoami:output_type -> littlehorse.Principal
+	86,  // 277: littlehorse.LittleHorse.GetServerVersion:output_type -> littlehorse.ServerVersion
+	203, // [203:278] is the sub-list for method output_type
+	128, // [128:203] is the sub-list for method input_type
 	128, // [128:128] is the sub-list for extension type_name
 	128, // [128:128] is the sub-list for extension extendee
 	0,   // [0:128] is the sub-list for field type_name
diff --git a/sdk-go/lhproto/service_grpc.pb.go b/sdk-go/lhproto/service_grpc.pb.go
index 2a184b411..75c513723 100644
--- a/sdk-go/lhproto/service_grpc.pb.go
+++ b/sdk-go/lhproto/service_grpc.pb.go
@@ -92,6 +92,7 @@ const (
 	LittleHorse_PutTenant_FullMethodName               = "/littlehorse.LittleHorse/PutTenant"
 	LittleHorse_GetTenant_FullMethodName               = "/littlehorse.LittleHorse/GetTenant"
 	LittleHorse_PutPrincipal_FullMethodName            = "/littlehorse.LittleHorse/PutPrincipal"
+	LittleHorse_GetPrincipal_FullMethodName            = "/littlehorse.LittleHorse/GetPrincipal"
 	LittleHorse_Whoami_FullMethodName                  = "/littlehorse.LittleHorse/Whoami"
 	LittleHorse_GetServerVersion_FullMethodName        = "/littlehorse.LittleHorse/GetServerVersion"
 )
@@ -299,6 +300,7 @@ type LittleHorseClient interface {
 	GetTenant(ctx context.Context, in *TenantId, opts ...grpc.CallOption) (*Tenant, error)
 	// EXPERIMENTAL: Creates an Principal.
 	PutPrincipal(ctx context.Context, in *PutPrincipalRequest, opts ...grpc.CallOption) (*Principal, error)
+	GetPrincipal(ctx context.Context, in *PrincipalId, opts ...grpc.CallOption) (*Principal, error)
 	// Returns the Principal of the caller.
 	Whoami(ctx context.Context, in *emptypb.Empty, opts ...grpc.CallOption) (*Principal, error)
 	// Gets the version of the LH Server.
@@ -983,6 +985,15 @@ func (c *littleHorseClient) PutPrincipal(ctx context.Context, in *PutPrincipalRe
 	return out, nil
 }
 
+func (c *littleHorseClient) GetPrincipal(ctx context.Context, in *PrincipalId, opts ...grpc.CallOption) (*Principal, error) {
+	out := new(Principal)
+	err := c.cc.Invoke(ctx, LittleHorse_GetPrincipal_FullMethodName, in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 func (c *littleHorseClient) Whoami(ctx context.Context, in *emptypb.Empty, opts ...grpc.CallOption) (*Principal, error) {
 	out := new(Principal)
 	err := c.cc.Invoke(ctx, LittleHorse_Whoami_FullMethodName, in, out, opts...)
@@ -1204,6 +1215,7 @@ type LittleHorseServer interface {
 	GetTenant(context.Context, *TenantId) (*Tenant, error)
 	// EXPERIMENTAL: Creates an Principal.
 	PutPrincipal(context.Context, *PutPrincipalRequest) (*Principal, error)
+	GetPrincipal(context.Context, *PrincipalId) (*Principal, error)
 	// Returns the Principal of the caller.
 	Whoami(context.Context, *emptypb.Empty) (*Principal, error)
 	// Gets the version of the LH Server.
@@ -1431,6 +1443,9 @@ func (UnimplementedLittleHorseServer) GetTenant(context.Context, *TenantId) (*Te
 func (UnimplementedLittleHorseServer) PutPrincipal(context.Context, *PutPrincipalRequest) (*Principal, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method PutPrincipal not implemented")
 }
+func (UnimplementedLittleHorseServer) GetPrincipal(context.Context, *PrincipalId) (*Principal, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method GetPrincipal not implemented")
+}
 func (UnimplementedLittleHorseServer) Whoami(context.Context, *emptypb.Empty) (*Principal, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method Whoami not implemented")
 }
@@ -2754,6 +2769,24 @@ func _LittleHorse_PutPrincipal_Handler(srv interface{}, ctx context.Context, dec
 	return interceptor(ctx, in, info, handler)
 }
 
+func _LittleHorse_GetPrincipal_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(PrincipalId)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(LittleHorseServer).GetPrincipal(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: LittleHorse_GetPrincipal_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(LittleHorseServer).GetPrincipal(ctx, req.(*PrincipalId))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
 func _LittleHorse_Whoami_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
 	in := new(emptypb.Empty)
 	if err := dec(in); err != nil {
@@ -3081,6 +3114,10 @@ var LittleHorse_ServiceDesc = grpc.ServiceDesc{
 			MethodName: "PutPrincipal",
 			Handler:    _LittleHorse_PutPrincipal_Handler,
 		},
+		{
+			MethodName: "GetPrincipal",
+			Handler:    _LittleHorse_GetPrincipal_Handler,
+		},
 		{
 			MethodName: "Whoami",
 			Handler:    _LittleHorse_Whoami_Handler,
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/CommonWfspec.java b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/CommonWfspec.java
index d571bd179..0406587c2 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/CommonWfspec.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/CommonWfspec.java
@@ -29,6 +29,11 @@ public static void registerAllExtensions(
   static final 
     com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
       internal_static_littlehorse_VariableAssignment_NodeOutputReference_fieldAccessorTable;
+  static final com.google.protobuf.Descriptors.Descriptor
+    internal_static_littlehorse_VariableAssignment_Expression_descriptor;
+  static final 
+    com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+      internal_static_littlehorse_VariableAssignment_Expression_fieldAccessorTable;
   static final com.google.protobuf.Descriptors.Descriptor
     internal_static_littlehorse_VariableMutation_descriptor;
   static final 
@@ -85,68 +90,73 @@ public static void registerAllExtensions(
     java.lang.String[] descriptorData = {
       "\n\023common_wfspec.proto\022\013littlehorse\032\022comm" +
       "on_enums.proto\032\016variable.proto\032\017object_i" +
-      "d.proto\"\277\003\n\022VariableAssignment\022\026\n\tjson_p" +
+      "d.proto\"\242\005\n\022VariableAssignment\022\026\n\tjson_p" +
       "ath\030\001 \001(\tH\001\210\001\001\022\027\n\rvariable_name\030\002 \001(\tH\000\022" +
       "3\n\rliteral_value\030\003 \001(\0132\032.littlehorse.Var" +
       "iableValueH\000\022E\n\rformat_string\030\004 \001(\0132,.li" +
       "ttlehorse.VariableAssignment.FormatStrin" +
       "gH\000\022J\n\013node_output\030\005 \001(\01323.littlehorse.V" +
-      "ariableAssignment.NodeOutputReferenceH\000\032" +
-      "n\n\014FormatString\022/\n\006format\030\001 \001(\0132\037.little" +
-      "horse.VariableAssignment\022-\n\004args\030\002 \003(\0132\037" +
-      ".littlehorse.VariableAssignment\032(\n\023NodeO" +
-      "utputReference\022\021\n\tnode_name\030\001 \001(\tB\010\n\006sou" +
-      "rceB\014\n\n_json_path\"\205\003\n\020VariableMutation\022\020" +
-      "\n\010lhs_name\030\001 \001(\t\022\032\n\rlhs_json_path\030\002 \001(\tH" +
-      "\001\210\001\001\0224\n\toperation\030\003 \001(\0162!.littlehorse.Va" +
-      "riableMutationType\022:\n\017source_variable\030\004 " +
-      "\001(\0132\037.littlehorse.VariableAssignmentH\000\0223" +
-      "\n\rliteral_value\030\005 \001(\0132\032.littlehorse.Vari" +
-      "ableValueH\000\022E\n\013node_output\030\006 \001(\0132..littl" +
-      "ehorse.VariableMutation.NodeOutputSource" +
-      "H\000\0326\n\020NodeOutputSource\022\025\n\010jsonpath\030\n \001(\t" +
-      "H\000\210\001\001B\013\n\t_jsonpathB\013\n\trhs_valueB\020\n\016_lhs_" +
-      "json_path\"\244\001\n\013VariableDef\022\'\n\004type\030\001 \001(\0162" +
-      "\031.littlehorse.VariableType\022\014\n\004name\030\002 \001(\t" +
-      "\0226\n\rdefault_value\030\003 \001(\0132\032.littlehorse.Va" +
-      "riableValueH\000\210\001\001\022\024\n\014masked_value\030\004 \001(\010B\020" +
-      "\n\016_default_value\"\357\004\n\017UTActionTrigger\0224\n\004" +
-      "task\030\001 \001(\0132$.littlehorse.UTActionTrigger" +
-      ".UTATaskH\000\0228\n\006cancel\030\002 \001(\0132&.littlehorse" +
-      ".UTActionTrigger.UTACancelH\000\022<\n\010reassign" +
-      "\030\003 \001(\0132(.littlehorse.UTActionTrigger.UTA" +
-      "ReassignH\000\0226\n\rdelay_seconds\030\005 \001(\0132\037.litt" +
-      "lehorse.VariableAssignment\0221\n\004hook\030\006 \001(\016" +
-      "2#.littlehorse.UTActionTrigger.UTHook\032\013\n" +
-      "\tUTACancel\032`\n\007UTATask\022#\n\004task\030\001 \001(\0132\025.li" +
-      "ttlehorse.TaskNode\0220\n\tmutations\030\002 \003(\0132\035." +
-      "littlehorse.VariableMutation\032\231\001\n\013UTAReas" +
-      "sign\0225\n\007user_id\030\001 \001(\0132\037.littlehorse.Vari" +
-      "ableAssignmentH\000\210\001\001\0228\n\nuser_group\030\002 \001(\0132" +
-      "\037.littlehorse.VariableAssignmentH\001\210\001\001B\n\n" +
-      "\010_user_idB\r\n\013_user_group\".\n\006UTHook\022\016\n\nON" +
-      "_ARRIVAL\020\000\022\024\n\020ON_TASK_ASSIGNED\020\001B\010\n\006acti" +
-      "on\"c\n\035ExponentialBackoffRetryPolicy\022\030\n\020b" +
-      "ase_interval_ms\030\001 \001(\005\022\024\n\014max_delay_ms\030\002 " +
-      "\001(\003\022\022\n\nmultiplier\030\003 \001(\002\"\311\002\n\010TaskNode\022-\n\013" +
-      "task_def_id\030\001 \001(\0132\026.littlehorse.TaskDefI" +
-      "dH\000\0227\n\014dynamic_task\030\006 \001(\0132\037.littlehorse." +
-      "VariableAssignmentH\000\022\027\n\017timeout_seconds\030" +
-      "\002 \001(\005\022\017\n\007retries\030\003 \001(\005\022L\n\023exponential_ba" +
-      "ckoff\030\005 \001(\0132*.littlehorse.ExponentialBac" +
-      "koffRetryPolicyH\001\210\001\001\0222\n\tvariables\030\004 \003(\0132" +
-      "\037.littlehorse.VariableAssignmentB\021\n\017task" +
-      "_to_executeB\026\n\024_exponential_backoff*\230\001\n\024" +
-      "VariableMutationType\022\n\n\006ASSIGN\020\000\022\007\n\003ADD\020" +
-      "\001\022\n\n\006EXTEND\020\002\022\014\n\010SUBTRACT\020\003\022\014\n\010MULTIPLY\020" +
-      "\004\022\n\n\006DIVIDE\020\005\022\025\n\021REMOVE_IF_PRESENT\020\006\022\020\n\014" +
-      "REMOVE_INDEX\020\007\022\016\n\nREMOVE_KEY\020\010*\204\001\n\nCompa" +
-      "rator\022\r\n\tLESS_THAN\020\000\022\020\n\014GREATER_THAN\020\001\022\020" +
-      "\n\014LESS_THAN_EQ\020\002\022\023\n\017GREATER_THAN_EQ\020\003\022\n\n" +
-      "\006EQUALS\020\004\022\016\n\nNOT_EQUALS\020\005\022\006\n\002IN\020\006\022\n\n\006NOT" +
-      "_IN\020\007BI\n\037io.littlehorse.sdk.common.proto" +
-      "P\001Z\t.;lhproto\252\002\030LittleHorse.Common.Proto" +
-      "b\006proto3"
+      "ariableAssignment.NodeOutputReferenceH\000\022" +
+      "@\n\nexpression\030\006 \001(\0132*.littlehorse.Variab" +
+      "leAssignment.ExpressionH\000\032n\n\014FormatStrin" +
+      "g\022/\n\006format\030\001 \001(\0132\037.littlehorse.Variable" +
+      "Assignment\022-\n\004args\030\002 \003(\0132\037.littlehorse.V" +
+      "ariableAssignment\032(\n\023NodeOutputReference" +
+      "\022\021\n\tnode_name\030\001 \001(\t\032\236\001\n\nExpression\022,\n\003lh" +
+      "s\030\001 \001(\0132\037.littlehorse.VariableAssignment" +
+      "\0224\n\toperation\030\002 \001(\0162!.littlehorse.Variab" +
+      "leMutationType\022,\n\003rhs\030\003 \001(\0132\037.littlehors" +
+      "e.VariableAssignmentB\010\n\006sourceB\014\n\n_json_" +
+      "path\"\205\003\n\020VariableMutation\022\020\n\010lhs_name\030\001 " +
+      "\001(\t\022\032\n\rlhs_json_path\030\002 \001(\tH\001\210\001\001\0224\n\topera" +
+      "tion\030\003 \001(\0162!.littlehorse.VariableMutatio" +
+      "nType\022:\n\017source_variable\030\004 \001(\0132\037.littleh" +
+      "orse.VariableAssignmentH\000\0223\n\rliteral_val" +
+      "ue\030\005 \001(\0132\032.littlehorse.VariableValueH\000\022E" +
+      "\n\013node_output\030\006 \001(\0132..littlehorse.Variab" +
+      "leMutation.NodeOutputSourceH\000\0326\n\020NodeOut" +
+      "putSource\022\025\n\010jsonpath\030\n \001(\tH\000\210\001\001B\013\n\t_jso" +
+      "npathB\013\n\trhs_valueB\020\n\016_lhs_json_path\"\244\001\n" +
+      "\013VariableDef\022\'\n\004type\030\001 \001(\0162\031.littlehorse" +
+      ".VariableType\022\014\n\004name\030\002 \001(\t\0226\n\rdefault_v" +
+      "alue\030\003 \001(\0132\032.littlehorse.VariableValueH\000" +
+      "\210\001\001\022\024\n\014masked_value\030\004 \001(\010B\020\n\016_default_va" +
+      "lue\"\357\004\n\017UTActionTrigger\0224\n\004task\030\001 \001(\0132$." +
+      "littlehorse.UTActionTrigger.UTATaskH\000\0228\n" +
+      "\006cancel\030\002 \001(\0132&.littlehorse.UTActionTrig" +
+      "ger.UTACancelH\000\022<\n\010reassign\030\003 \001(\0132(.litt" +
+      "lehorse.UTActionTrigger.UTAReassignH\000\0226\n" +
+      "\rdelay_seconds\030\005 \001(\0132\037.littlehorse.Varia" +
+      "bleAssignment\0221\n\004hook\030\006 \001(\0162#.littlehors" +
+      "e.UTActionTrigger.UTHook\032\013\n\tUTACancel\032`\n" +
+      "\007UTATask\022#\n\004task\030\001 \001(\0132\025.littlehorse.Tas" +
+      "kNode\0220\n\tmutations\030\002 \003(\0132\035.littlehorse.V" +
+      "ariableMutation\032\231\001\n\013UTAReassign\0225\n\007user_" +
+      "id\030\001 \001(\0132\037.littlehorse.VariableAssignmen" +
+      "tH\000\210\001\001\0228\n\nuser_group\030\002 \001(\0132\037.littlehorse" +
+      ".VariableAssignmentH\001\210\001\001B\n\n\010_user_idB\r\n\013" +
+      "_user_group\".\n\006UTHook\022\016\n\nON_ARRIVAL\020\000\022\024\n" +
+      "\020ON_TASK_ASSIGNED\020\001B\010\n\006action\"c\n\035Exponen" +
+      "tialBackoffRetryPolicy\022\030\n\020base_interval_" +
+      "ms\030\001 \001(\005\022\024\n\014max_delay_ms\030\002 \001(\003\022\022\n\nmultip" +
+      "lier\030\003 \001(\002\"\311\002\n\010TaskNode\022-\n\013task_def_id\030\001" +
+      " \001(\0132\026.littlehorse.TaskDefIdH\000\0227\n\014dynami" +
+      "c_task\030\006 \001(\0132\037.littlehorse.VariableAssig" +
+      "nmentH\000\022\027\n\017timeout_seconds\030\002 \001(\005\022\017\n\007retr" +
+      "ies\030\003 \001(\005\022L\n\023exponential_backoff\030\005 \001(\0132*" +
+      ".littlehorse.ExponentialBackoffRetryPoli" +
+      "cyH\001\210\001\001\0222\n\tvariables\030\004 \003(\0132\037.littlehorse" +
+      ".VariableAssignmentB\021\n\017task_to_executeB\026" +
+      "\n\024_exponential_backoff*\230\001\n\024VariableMutat" +
+      "ionType\022\n\n\006ASSIGN\020\000\022\007\n\003ADD\020\001\022\n\n\006EXTEND\020\002" +
+      "\022\014\n\010SUBTRACT\020\003\022\014\n\010MULTIPLY\020\004\022\n\n\006DIVIDE\020\005" +
+      "\022\025\n\021REMOVE_IF_PRESENT\020\006\022\020\n\014REMOVE_INDEX\020" +
+      "\007\022\016\n\nREMOVE_KEY\020\010*\204\001\n\nComparator\022\r\n\tLESS" +
+      "_THAN\020\000\022\020\n\014GREATER_THAN\020\001\022\020\n\014LESS_THAN_E" +
+      "Q\020\002\022\023\n\017GREATER_THAN_EQ\020\003\022\n\n\006EQUALS\020\004\022\016\n\n" +
+      "NOT_EQUALS\020\005\022\006\n\002IN\020\006\022\n\n\006NOT_IN\020\007BI\n\037io.l" +
+      "ittlehorse.sdk.common.protoP\001Z\t.;lhproto" +
+      "\252\002\030LittleHorse.Common.Protob\006proto3"
     };
     descriptor = com.google.protobuf.Descriptors.FileDescriptor
       .internalBuildGeneratedFileFrom(descriptorData,
@@ -160,7 +170,7 @@ public static void registerAllExtensions(
     internal_static_littlehorse_VariableAssignment_fieldAccessorTable = new
       com.google.protobuf.GeneratedMessageV3.FieldAccessorTable(
         internal_static_littlehorse_VariableAssignment_descriptor,
-        new java.lang.String[] { "JsonPath", "VariableName", "LiteralValue", "FormatString", "NodeOutput", "Source", "JsonPath", });
+        new java.lang.String[] { "JsonPath", "VariableName", "LiteralValue", "FormatString", "NodeOutput", "Expression", "Source", "JsonPath", });
     internal_static_littlehorse_VariableAssignment_FormatString_descriptor =
       internal_static_littlehorse_VariableAssignment_descriptor.getNestedTypes().get(0);
     internal_static_littlehorse_VariableAssignment_FormatString_fieldAccessorTable = new
@@ -173,6 +183,12 @@ public static void registerAllExtensions(
       com.google.protobuf.GeneratedMessageV3.FieldAccessorTable(
         internal_static_littlehorse_VariableAssignment_NodeOutputReference_descriptor,
         new java.lang.String[] { "NodeName", });
+    internal_static_littlehorse_VariableAssignment_Expression_descriptor =
+      internal_static_littlehorse_VariableAssignment_descriptor.getNestedTypes().get(2);
+    internal_static_littlehorse_VariableAssignment_Expression_fieldAccessorTable = new
+      com.google.protobuf.GeneratedMessageV3.FieldAccessorTable(
+        internal_static_littlehorse_VariableAssignment_Expression_descriptor,
+        new java.lang.String[] { "Lhs", "Operation", "Rhs", });
     internal_static_littlehorse_VariableMutation_descriptor =
       getDescriptor().getMessageTypes().get(1);
     internal_static_littlehorse_VariableMutation_fieldAccessorTable = new
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/LittleHorseGrpc.java b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/LittleHorseGrpc.java
index bbc582e35..0c810179c 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/LittleHorseGrpc.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/LittleHorseGrpc.java
@@ -2247,6 +2247,37 @@ io.littlehorse.sdk.common.proto.Principal> getPutPrincipalMethod() {
     return getPutPrincipalMethod;
   }
 
+  private static volatile io.grpc.MethodDescriptor<io.littlehorse.sdk.common.proto.PrincipalId,
+      io.littlehorse.sdk.common.proto.Principal> getGetPrincipalMethod;
+
+  @io.grpc.stub.annotations.RpcMethod(
+      fullMethodName = SERVICE_NAME + '/' + "GetPrincipal",
+      requestType = io.littlehorse.sdk.common.proto.PrincipalId.class,
+      responseType = io.littlehorse.sdk.common.proto.Principal.class,
+      methodType = io.grpc.MethodDescriptor.MethodType.UNARY)
+  public static io.grpc.MethodDescriptor<io.littlehorse.sdk.common.proto.PrincipalId,
+      io.littlehorse.sdk.common.proto.Principal> getGetPrincipalMethod() {
+    io.grpc.MethodDescriptor<io.littlehorse.sdk.common.proto.PrincipalId, io.littlehorse.sdk.common.proto.Principal> getGetPrincipalMethod;
+    if ((getGetPrincipalMethod = LittleHorseGrpc.getGetPrincipalMethod) == null) {
+      synchronized (LittleHorseGrpc.class) {
+        if ((getGetPrincipalMethod = LittleHorseGrpc.getGetPrincipalMethod) == null) {
+          LittleHorseGrpc.getGetPrincipalMethod = getGetPrincipalMethod =
+              io.grpc.MethodDescriptor.<io.littlehorse.sdk.common.proto.PrincipalId, io.littlehorse.sdk.common.proto.Principal>newBuilder()
+              .setType(io.grpc.MethodDescriptor.MethodType.UNARY)
+              .setFullMethodName(generateFullMethodName(SERVICE_NAME, "GetPrincipal"))
+              .setSampledToLocalTracing(true)
+              .setRequestMarshaller(io.grpc.protobuf.ProtoUtils.marshaller(
+                  io.littlehorse.sdk.common.proto.PrincipalId.getDefaultInstance()))
+              .setResponseMarshaller(io.grpc.protobuf.ProtoUtils.marshaller(
+                  io.littlehorse.sdk.common.proto.Principal.getDefaultInstance()))
+              .setSchemaDescriptor(new LittleHorseMethodDescriptorSupplier("GetPrincipal"))
+              .build();
+        }
+      }
+    }
+    return getGetPrincipalMethod;
+  }
+
   private static volatile io.grpc.MethodDescriptor<com.google.protobuf.Empty,
       io.littlehorse.sdk.common.proto.Principal> getWhoamiMethod;
 
@@ -3119,6 +3150,13 @@ default void putPrincipal(io.littlehorse.sdk.common.proto.PutPrincipalRequest re
       io.grpc.stub.ServerCalls.asyncUnimplementedUnaryCall(getPutPrincipalMethod(), responseObserver);
     }
 
+    /**
+     */
+    default void getPrincipal(io.littlehorse.sdk.common.proto.PrincipalId request,
+        io.grpc.stub.StreamObserver<io.littlehorse.sdk.common.proto.Principal> responseObserver) {
+      io.grpc.stub.ServerCalls.asyncUnimplementedUnaryCall(getGetPrincipalMethod(), responseObserver);
+    }
+
     /**
      * <pre>
      * Returns the Principal of the caller.
@@ -4001,6 +4039,14 @@ public void putPrincipal(io.littlehorse.sdk.common.proto.PutPrincipalRequest req
           getChannel().newCall(getPutPrincipalMethod(), getCallOptions()), request, responseObserver);
     }
 
+    /**
+     */
+    public void getPrincipal(io.littlehorse.sdk.common.proto.PrincipalId request,
+        io.grpc.stub.StreamObserver<io.littlehorse.sdk.common.proto.Principal> responseObserver) {
+      io.grpc.stub.ClientCalls.asyncUnaryCall(
+          getChannel().newCall(getGetPrincipalMethod(), getCallOptions()), request, responseObserver);
+    }
+
     /**
      * <pre>
      * Returns the Principal of the caller.
@@ -4791,6 +4837,13 @@ public io.littlehorse.sdk.common.proto.Principal putPrincipal(io.littlehorse.sdk
           getChannel(), getPutPrincipalMethod(), getCallOptions(), request);
     }
 
+    /**
+     */
+    public io.littlehorse.sdk.common.proto.Principal getPrincipal(io.littlehorse.sdk.common.proto.PrincipalId request) {
+      return io.grpc.stub.ClientCalls.blockingUnaryCall(
+          getChannel(), getGetPrincipalMethod(), getCallOptions(), request);
+    }
+
     /**
      * <pre>
      * Returns the Principal of the caller.
@@ -5650,6 +5703,14 @@ public com.google.common.util.concurrent.ListenableFuture<io.littlehorse.sdk.com
           getChannel().newCall(getPutPrincipalMethod(), getCallOptions()), request);
     }
 
+    /**
+     */
+    public com.google.common.util.concurrent.ListenableFuture<io.littlehorse.sdk.common.proto.Principal> getPrincipal(
+        io.littlehorse.sdk.common.proto.PrincipalId request) {
+      return io.grpc.stub.ClientCalls.futureUnaryCall(
+          getChannel().newCall(getGetPrincipalMethod(), getCallOptions()), request);
+    }
+
     /**
      * <pre>
      * Returns the Principal of the caller.
@@ -5744,9 +5805,10 @@ public com.google.common.util.concurrent.ListenableFuture<io.littlehorse.sdk.com
   private static final int METHODID_PUT_TENANT = 68;
   private static final int METHODID_GET_TENANT = 69;
   private static final int METHODID_PUT_PRINCIPAL = 70;
-  private static final int METHODID_WHOAMI = 71;
-  private static final int METHODID_GET_SERVER_VERSION = 72;
-  private static final int METHODID_POLL_TASK = 73;
+  private static final int METHODID_GET_PRINCIPAL = 71;
+  private static final int METHODID_WHOAMI = 72;
+  private static final int METHODID_GET_SERVER_VERSION = 73;
+  private static final int METHODID_POLL_TASK = 74;
 
   private static final class MethodHandlers<Req, Resp> implements
       io.grpc.stub.ServerCalls.UnaryMethod<Req, Resp>,
@@ -6049,6 +6111,10 @@ public void invoke(Req request, io.grpc.stub.StreamObserver<Resp> responseObserv
           serviceImpl.putPrincipal((io.littlehorse.sdk.common.proto.PutPrincipalRequest) request,
               (io.grpc.stub.StreamObserver<io.littlehorse.sdk.common.proto.Principal>) responseObserver);
           break;
+        case METHODID_GET_PRINCIPAL:
+          serviceImpl.getPrincipal((io.littlehorse.sdk.common.proto.PrincipalId) request,
+              (io.grpc.stub.StreamObserver<io.littlehorse.sdk.common.proto.Principal>) responseObserver);
+          break;
         case METHODID_WHOAMI:
           serviceImpl.whoami((com.google.protobuf.Empty) request,
               (io.grpc.stub.StreamObserver<io.littlehorse.sdk.common.proto.Principal>) responseObserver);
@@ -6582,6 +6648,13 @@ public static final io.grpc.ServerServiceDefinition bindService(AsyncService ser
               io.littlehorse.sdk.common.proto.PutPrincipalRequest,
               io.littlehorse.sdk.common.proto.Principal>(
                 service, METHODID_PUT_PRINCIPAL)))
+        .addMethod(
+          getGetPrincipalMethod(),
+          io.grpc.stub.ServerCalls.asyncUnaryCall(
+            new MethodHandlers<
+              io.littlehorse.sdk.common.proto.PrincipalId,
+              io.littlehorse.sdk.common.proto.Principal>(
+                service, METHODID_GET_PRINCIPAL)))
         .addMethod(
           getWhoamiMethod(),
           io.grpc.stub.ServerCalls.asyncUnaryCall(
@@ -6716,6 +6789,7 @@ public static io.grpc.ServiceDescriptor getServiceDescriptor() {
               .addMethod(getPutTenantMethod())
               .addMethod(getGetTenantMethod())
               .addMethod(getPutPrincipalMethod())
+              .addMethod(getGetPrincipalMethod())
               .addMethod(getWhoamiMethod())
               .addMethod(getGetServerVersionMethod())
               .build();
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/Service.java b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/Service.java
index 75b041c3a..ae4988cdf 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/Service.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/Service.java
@@ -806,7 +806,7 @@ public static void registerAllExtensions(
       "se_identifier\030\004 \001(\tH\000\210\001\001B\031\n\027_pre_release" +
       "_identifier*P\n\021AllowedUpdateType\022\017\n\013ALL_" +
       "UPDATES\020\000\022\032\n\026MINOR_REVISION_UPDATES\020\001\022\016\n" +
-      "\nNO_UPDATES\020\0022\352/\n\013LittleHorse\022D\n\nPutTask" +
+      "\nNO_UPDATES\020\0022\2560\n\013LittleHorse\022D\n\nPutTask" +
       "Def\022\036.littlehorse.PutTaskDefRequest\032\024.li" +
       "ttlehorse.TaskDef\"\000\022<\n\nGetTaskDef\022\026.litt" +
       "lehorse.TaskDefId\032\024.littlehorse.TaskDef\"" +
@@ -956,12 +956,14 @@ public static void registerAllExtensions(
       "nt\022\025.littlehorse.TenantId\032\023.littlehorse." +
       "Tenant\"\000\022J\n\014PutPrincipal\022 .littlehorse.P" +
       "utPrincipalRequest\032\026.littlehorse.Princip" +
-      "al\"\000\022:\n\006Whoami\022\026.google.protobuf.Empty\032\026" +
-      ".littlehorse.Principal\"\000\022H\n\020GetServerVer" +
-      "sion\022\026.google.protobuf.Empty\032\032.littlehor" +
-      "se.ServerVersion\"\000BI\n\037io.littlehorse.sdk" +
-      ".common.protoP\001Z\t.;lhproto\252\002\030LittleHorse" +
-      ".Common.Protob\006proto3"
+      "al\"\000\022B\n\014GetPrincipal\022\030.littlehorse.Princ" +
+      "ipalId\032\026.littlehorse.Principal\"\000\022:\n\006Whoa" +
+      "mi\022\026.google.protobuf.Empty\032\026.littlehorse" +
+      ".Principal\"\000\022H\n\020GetServerVersion\022\026.googl" +
+      "e.protobuf.Empty\032\032.littlehorse.ServerVer" +
+      "sion\"\000BI\n\037io.littlehorse.sdk.common.prot" +
+      "oP\001Z\t.;lhproto\252\002\030LittleHorse.Common.Prot" +
+      "ob\006proto3"
     };
     descriptor = com.google.protobuf.Descriptors.FileDescriptor
       .internalBuildGeneratedFileFrom(descriptorData,
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignment.java b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignment.java
index d3495e3a4..170fd87d2 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignment.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignment.java
@@ -1824,6 +1824,1071 @@ public io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReference ge
 
   }
 
+  public interface ExpressionOrBuilder extends
+      // @@protoc_insertion_point(interface_extends:littlehorse.VariableAssignment.Expression)
+      com.google.protobuf.MessageOrBuilder {
+
+    /**
+     * <pre>
+     * The left-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+     * @return Whether the lhs field is set.
+     */
+    boolean hasLhs();
+    /**
+     * <pre>
+     * The left-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+     * @return The lhs.
+     */
+    io.littlehorse.sdk.common.proto.VariableAssignment getLhs();
+    /**
+     * <pre>
+     * The left-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+     */
+    io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder getLhsOrBuilder();
+
+    /**
+     * <pre>
+     * The operator in the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableMutationType operation = 2;</code>
+     * @return The enum numeric value on the wire for operation.
+     */
+    int getOperationValue();
+    /**
+     * <pre>
+     * The operator in the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableMutationType operation = 2;</code>
+     * @return The operation.
+     */
+    io.littlehorse.sdk.common.proto.VariableMutationType getOperation();
+
+    /**
+     * <pre>
+     * The right-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+     * @return Whether the rhs field is set.
+     */
+    boolean hasRhs();
+    /**
+     * <pre>
+     * The right-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+     * @return The rhs.
+     */
+    io.littlehorse.sdk.common.proto.VariableAssignment getRhs();
+    /**
+     * <pre>
+     * The right-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+     */
+    io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder getRhsOrBuilder();
+  }
+  /**
+   * <pre>
+   * An Expression allows you to combine multiple values into one.
+   * </pre>
+   *
+   * Protobuf type {@code littlehorse.VariableAssignment.Expression}
+   */
+  public static final class Expression extends
+      com.google.protobuf.GeneratedMessageV3 implements
+      // @@protoc_insertion_point(message_implements:littlehorse.VariableAssignment.Expression)
+      ExpressionOrBuilder {
+  private static final long serialVersionUID = 0L;
+    // Use Expression.newBuilder() to construct.
+    private Expression(com.google.protobuf.GeneratedMessageV3.Builder<?> builder) {
+      super(builder);
+    }
+    private Expression() {
+      operation_ = 0;
+    }
+
+    @java.lang.Override
+    @SuppressWarnings({"unused"})
+    protected java.lang.Object newInstance(
+        UnusedPrivateParameter unused) {
+      return new Expression();
+    }
+
+    public static final com.google.protobuf.Descriptors.Descriptor
+        getDescriptor() {
+      return io.littlehorse.sdk.common.proto.CommonWfspec.internal_static_littlehorse_VariableAssignment_Expression_descriptor;
+    }
+
+    @java.lang.Override
+    protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+        internalGetFieldAccessorTable() {
+      return io.littlehorse.sdk.common.proto.CommonWfspec.internal_static_littlehorse_VariableAssignment_Expression_fieldAccessorTable
+          .ensureFieldAccessorsInitialized(
+              io.littlehorse.sdk.common.proto.VariableAssignment.Expression.class, io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder.class);
+    }
+
+    public static final int LHS_FIELD_NUMBER = 1;
+    private io.littlehorse.sdk.common.proto.VariableAssignment lhs_;
+    /**
+     * <pre>
+     * The left-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+     * @return Whether the lhs field is set.
+     */
+    @java.lang.Override
+    public boolean hasLhs() {
+      return lhs_ != null;
+    }
+    /**
+     * <pre>
+     * The left-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+     * @return The lhs.
+     */
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignment getLhs() {
+      return lhs_ == null ? io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : lhs_;
+    }
+    /**
+     * <pre>
+     * The left-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+     */
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder getLhsOrBuilder() {
+      return lhs_ == null ? io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : lhs_;
+    }
+
+    public static final int OPERATION_FIELD_NUMBER = 2;
+    private int operation_ = 0;
+    /**
+     * <pre>
+     * The operator in the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableMutationType operation = 2;</code>
+     * @return The enum numeric value on the wire for operation.
+     */
+    @java.lang.Override public int getOperationValue() {
+      return operation_;
+    }
+    /**
+     * <pre>
+     * The operator in the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableMutationType operation = 2;</code>
+     * @return The operation.
+     */
+    @java.lang.Override public io.littlehorse.sdk.common.proto.VariableMutationType getOperation() {
+      io.littlehorse.sdk.common.proto.VariableMutationType result = io.littlehorse.sdk.common.proto.VariableMutationType.forNumber(operation_);
+      return result == null ? io.littlehorse.sdk.common.proto.VariableMutationType.UNRECOGNIZED : result;
+    }
+
+    public static final int RHS_FIELD_NUMBER = 3;
+    private io.littlehorse.sdk.common.proto.VariableAssignment rhs_;
+    /**
+     * <pre>
+     * The right-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+     * @return Whether the rhs field is set.
+     */
+    @java.lang.Override
+    public boolean hasRhs() {
+      return rhs_ != null;
+    }
+    /**
+     * <pre>
+     * The right-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+     * @return The rhs.
+     */
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignment getRhs() {
+      return rhs_ == null ? io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : rhs_;
+    }
+    /**
+     * <pre>
+     * The right-hand-side of the expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+     */
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder getRhsOrBuilder() {
+      return rhs_ == null ? io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : rhs_;
+    }
+
+    private byte memoizedIsInitialized = -1;
+    @java.lang.Override
+    public final boolean isInitialized() {
+      byte isInitialized = memoizedIsInitialized;
+      if (isInitialized == 1) return true;
+      if (isInitialized == 0) return false;
+
+      memoizedIsInitialized = 1;
+      return true;
+    }
+
+    @java.lang.Override
+    public void writeTo(com.google.protobuf.CodedOutputStream output)
+                        throws java.io.IOException {
+      if (lhs_ != null) {
+        output.writeMessage(1, getLhs());
+      }
+      if (operation_ != io.littlehorse.sdk.common.proto.VariableMutationType.ASSIGN.getNumber()) {
+        output.writeEnum(2, operation_);
+      }
+      if (rhs_ != null) {
+        output.writeMessage(3, getRhs());
+      }
+      getUnknownFields().writeTo(output);
+    }
+
+    @java.lang.Override
+    public int getSerializedSize() {
+      int size = memoizedSize;
+      if (size != -1) return size;
+
+      size = 0;
+      if (lhs_ != null) {
+        size += com.google.protobuf.CodedOutputStream
+          .computeMessageSize(1, getLhs());
+      }
+      if (operation_ != io.littlehorse.sdk.common.proto.VariableMutationType.ASSIGN.getNumber()) {
+        size += com.google.protobuf.CodedOutputStream
+          .computeEnumSize(2, operation_);
+      }
+      if (rhs_ != null) {
+        size += com.google.protobuf.CodedOutputStream
+          .computeMessageSize(3, getRhs());
+      }
+      size += getUnknownFields().getSerializedSize();
+      memoizedSize = size;
+      return size;
+    }
+
+    @java.lang.Override
+    public boolean equals(final java.lang.Object obj) {
+      if (obj == this) {
+       return true;
+      }
+      if (!(obj instanceof io.littlehorse.sdk.common.proto.VariableAssignment.Expression)) {
+        return super.equals(obj);
+      }
+      io.littlehorse.sdk.common.proto.VariableAssignment.Expression other = (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) obj;
+
+      if (hasLhs() != other.hasLhs()) return false;
+      if (hasLhs()) {
+        if (!getLhs()
+            .equals(other.getLhs())) return false;
+      }
+      if (operation_ != other.operation_) return false;
+      if (hasRhs() != other.hasRhs()) return false;
+      if (hasRhs()) {
+        if (!getRhs()
+            .equals(other.getRhs())) return false;
+      }
+      if (!getUnknownFields().equals(other.getUnknownFields())) return false;
+      return true;
+    }
+
+    @java.lang.Override
+    public int hashCode() {
+      if (memoizedHashCode != 0) {
+        return memoizedHashCode;
+      }
+      int hash = 41;
+      hash = (19 * hash) + getDescriptor().hashCode();
+      if (hasLhs()) {
+        hash = (37 * hash) + LHS_FIELD_NUMBER;
+        hash = (53 * hash) + getLhs().hashCode();
+      }
+      hash = (37 * hash) + OPERATION_FIELD_NUMBER;
+      hash = (53 * hash) + operation_;
+      if (hasRhs()) {
+        hash = (37 * hash) + RHS_FIELD_NUMBER;
+        hash = (53 * hash) + getRhs().hashCode();
+      }
+      hash = (29 * hash) + getUnknownFields().hashCode();
+      memoizedHashCode = hash;
+      return hash;
+    }
+
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        java.nio.ByteBuffer data)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return PARSER.parseFrom(data);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        java.nio.ByteBuffer data,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return PARSER.parseFrom(data, extensionRegistry);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        com.google.protobuf.ByteString data)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return PARSER.parseFrom(data);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        com.google.protobuf.ByteString data,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return PARSER.parseFrom(data, extensionRegistry);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(byte[] data)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return PARSER.parseFrom(data);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        byte[] data,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws com.google.protobuf.InvalidProtocolBufferException {
+      return PARSER.parseFrom(data, extensionRegistry);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(java.io.InputStream input)
+        throws java.io.IOException {
+      return com.google.protobuf.GeneratedMessageV3
+          .parseWithIOException(PARSER, input);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        java.io.InputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      return com.google.protobuf.GeneratedMessageV3
+          .parseWithIOException(PARSER, input, extensionRegistry);
+    }
+
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseDelimitedFrom(java.io.InputStream input)
+        throws java.io.IOException {
+      return com.google.protobuf.GeneratedMessageV3
+          .parseDelimitedWithIOException(PARSER, input);
+    }
+
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseDelimitedFrom(
+        java.io.InputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      return com.google.protobuf.GeneratedMessageV3
+          .parseDelimitedWithIOException(PARSER, input, extensionRegistry);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        com.google.protobuf.CodedInputStream input)
+        throws java.io.IOException {
+      return com.google.protobuf.GeneratedMessageV3
+          .parseWithIOException(PARSER, input);
+    }
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression parseFrom(
+        com.google.protobuf.CodedInputStream input,
+        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+        throws java.io.IOException {
+      return com.google.protobuf.GeneratedMessageV3
+          .parseWithIOException(PARSER, input, extensionRegistry);
+    }
+
+    @java.lang.Override
+    public Builder newBuilderForType() { return newBuilder(); }
+    public static Builder newBuilder() {
+      return DEFAULT_INSTANCE.toBuilder();
+    }
+    public static Builder newBuilder(io.littlehorse.sdk.common.proto.VariableAssignment.Expression prototype) {
+      return DEFAULT_INSTANCE.toBuilder().mergeFrom(prototype);
+    }
+    @java.lang.Override
+    public Builder toBuilder() {
+      return this == DEFAULT_INSTANCE
+          ? new Builder() : new Builder().mergeFrom(this);
+    }
+
+    @java.lang.Override
+    protected Builder newBuilderForType(
+        com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
+      Builder builder = new Builder(parent);
+      return builder;
+    }
+    /**
+     * <pre>
+     * An Expression allows you to combine multiple values into one.
+     * </pre>
+     *
+     * Protobuf type {@code littlehorse.VariableAssignment.Expression}
+     */
+    public static final class Builder extends
+        com.google.protobuf.GeneratedMessageV3.Builder<Builder> implements
+        // @@protoc_insertion_point(builder_implements:littlehorse.VariableAssignment.Expression)
+        io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder {
+      public static final com.google.protobuf.Descriptors.Descriptor
+          getDescriptor() {
+        return io.littlehorse.sdk.common.proto.CommonWfspec.internal_static_littlehorse_VariableAssignment_Expression_descriptor;
+      }
+
+      @java.lang.Override
+      protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+          internalGetFieldAccessorTable() {
+        return io.littlehorse.sdk.common.proto.CommonWfspec.internal_static_littlehorse_VariableAssignment_Expression_fieldAccessorTable
+            .ensureFieldAccessorsInitialized(
+                io.littlehorse.sdk.common.proto.VariableAssignment.Expression.class, io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder.class);
+      }
+
+      // Construct using io.littlehorse.sdk.common.proto.VariableAssignment.Expression.newBuilder()
+      private Builder() {
+
+      }
+
+      private Builder(
+          com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
+        super(parent);
+
+      }
+      @java.lang.Override
+      public Builder clear() {
+        super.clear();
+        bitField0_ = 0;
+        lhs_ = null;
+        if (lhsBuilder_ != null) {
+          lhsBuilder_.dispose();
+          lhsBuilder_ = null;
+        }
+        operation_ = 0;
+        rhs_ = null;
+        if (rhsBuilder_ != null) {
+          rhsBuilder_.dispose();
+          rhsBuilder_ = null;
+        }
+        return this;
+      }
+
+      @java.lang.Override
+      public com.google.protobuf.Descriptors.Descriptor
+          getDescriptorForType() {
+        return io.littlehorse.sdk.common.proto.CommonWfspec.internal_static_littlehorse_VariableAssignment_Expression_descriptor;
+      }
+
+      @java.lang.Override
+      public io.littlehorse.sdk.common.proto.VariableAssignment.Expression getDefaultInstanceForType() {
+        return io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+      }
+
+      @java.lang.Override
+      public io.littlehorse.sdk.common.proto.VariableAssignment.Expression build() {
+        io.littlehorse.sdk.common.proto.VariableAssignment.Expression result = buildPartial();
+        if (!result.isInitialized()) {
+          throw newUninitializedMessageException(result);
+        }
+        return result;
+      }
+
+      @java.lang.Override
+      public io.littlehorse.sdk.common.proto.VariableAssignment.Expression buildPartial() {
+        io.littlehorse.sdk.common.proto.VariableAssignment.Expression result = new io.littlehorse.sdk.common.proto.VariableAssignment.Expression(this);
+        if (bitField0_ != 0) { buildPartial0(result); }
+        onBuilt();
+        return result;
+      }
+
+      private void buildPartial0(io.littlehorse.sdk.common.proto.VariableAssignment.Expression result) {
+        int from_bitField0_ = bitField0_;
+        if (((from_bitField0_ & 0x00000001) != 0)) {
+          result.lhs_ = lhsBuilder_ == null
+              ? lhs_
+              : lhsBuilder_.build();
+        }
+        if (((from_bitField0_ & 0x00000002) != 0)) {
+          result.operation_ = operation_;
+        }
+        if (((from_bitField0_ & 0x00000004) != 0)) {
+          result.rhs_ = rhsBuilder_ == null
+              ? rhs_
+              : rhsBuilder_.build();
+        }
+      }
+
+      @java.lang.Override
+      public Builder clone() {
+        return super.clone();
+      }
+      @java.lang.Override
+      public Builder setField(
+          com.google.protobuf.Descriptors.FieldDescriptor field,
+          java.lang.Object value) {
+        return super.setField(field, value);
+      }
+      @java.lang.Override
+      public Builder clearField(
+          com.google.protobuf.Descriptors.FieldDescriptor field) {
+        return super.clearField(field);
+      }
+      @java.lang.Override
+      public Builder clearOneof(
+          com.google.protobuf.Descriptors.OneofDescriptor oneof) {
+        return super.clearOneof(oneof);
+      }
+      @java.lang.Override
+      public Builder setRepeatedField(
+          com.google.protobuf.Descriptors.FieldDescriptor field,
+          int index, java.lang.Object value) {
+        return super.setRepeatedField(field, index, value);
+      }
+      @java.lang.Override
+      public Builder addRepeatedField(
+          com.google.protobuf.Descriptors.FieldDescriptor field,
+          java.lang.Object value) {
+        return super.addRepeatedField(field, value);
+      }
+      @java.lang.Override
+      public Builder mergeFrom(com.google.protobuf.Message other) {
+        if (other instanceof io.littlehorse.sdk.common.proto.VariableAssignment.Expression) {
+          return mergeFrom((io.littlehorse.sdk.common.proto.VariableAssignment.Expression)other);
+        } else {
+          super.mergeFrom(other);
+          return this;
+        }
+      }
+
+      public Builder mergeFrom(io.littlehorse.sdk.common.proto.VariableAssignment.Expression other) {
+        if (other == io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance()) return this;
+        if (other.hasLhs()) {
+          mergeLhs(other.getLhs());
+        }
+        if (other.operation_ != 0) {
+          setOperationValue(other.getOperationValue());
+        }
+        if (other.hasRhs()) {
+          mergeRhs(other.getRhs());
+        }
+        this.mergeUnknownFields(other.getUnknownFields());
+        onChanged();
+        return this;
+      }
+
+      @java.lang.Override
+      public final boolean isInitialized() {
+        return true;
+      }
+
+      @java.lang.Override
+      public Builder mergeFrom(
+          com.google.protobuf.CodedInputStream input,
+          com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+          throws java.io.IOException {
+        if (extensionRegistry == null) {
+          throw new java.lang.NullPointerException();
+        }
+        try {
+          boolean done = false;
+          while (!done) {
+            int tag = input.readTag();
+            switch (tag) {
+              case 0:
+                done = true;
+                break;
+              case 10: {
+                input.readMessage(
+                    getLhsFieldBuilder().getBuilder(),
+                    extensionRegistry);
+                bitField0_ |= 0x00000001;
+                break;
+              } // case 10
+              case 16: {
+                operation_ = input.readEnum();
+                bitField0_ |= 0x00000002;
+                break;
+              } // case 16
+              case 26: {
+                input.readMessage(
+                    getRhsFieldBuilder().getBuilder(),
+                    extensionRegistry);
+                bitField0_ |= 0x00000004;
+                break;
+              } // case 26
+              default: {
+                if (!super.parseUnknownField(input, extensionRegistry, tag)) {
+                  done = true; // was an endgroup tag
+                }
+                break;
+              } // default:
+            } // switch (tag)
+          } // while (!done)
+        } catch (com.google.protobuf.InvalidProtocolBufferException e) {
+          throw e.unwrapIOException();
+        } finally {
+          onChanged();
+        } // finally
+        return this;
+      }
+      private int bitField0_;
+
+      private io.littlehorse.sdk.common.proto.VariableAssignment lhs_;
+      private com.google.protobuf.SingleFieldBuilderV3<
+          io.littlehorse.sdk.common.proto.VariableAssignment, io.littlehorse.sdk.common.proto.VariableAssignment.Builder, io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder> lhsBuilder_;
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       * @return Whether the lhs field is set.
+       */
+      public boolean hasLhs() {
+        return ((bitField0_ & 0x00000001) != 0);
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       * @return The lhs.
+       */
+      public io.littlehorse.sdk.common.proto.VariableAssignment getLhs() {
+        if (lhsBuilder_ == null) {
+          return lhs_ == null ? io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : lhs_;
+        } else {
+          return lhsBuilder_.getMessage();
+        }
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      public Builder setLhs(io.littlehorse.sdk.common.proto.VariableAssignment value) {
+        if (lhsBuilder_ == null) {
+          if (value == null) {
+            throw new NullPointerException();
+          }
+          lhs_ = value;
+        } else {
+          lhsBuilder_.setMessage(value);
+        }
+        bitField0_ |= 0x00000001;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      public Builder setLhs(
+          io.littlehorse.sdk.common.proto.VariableAssignment.Builder builderForValue) {
+        if (lhsBuilder_ == null) {
+          lhs_ = builderForValue.build();
+        } else {
+          lhsBuilder_.setMessage(builderForValue.build());
+        }
+        bitField0_ |= 0x00000001;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      public Builder mergeLhs(io.littlehorse.sdk.common.proto.VariableAssignment value) {
+        if (lhsBuilder_ == null) {
+          if (((bitField0_ & 0x00000001) != 0) &&
+            lhs_ != null &&
+            lhs_ != io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance()) {
+            getLhsBuilder().mergeFrom(value);
+          } else {
+            lhs_ = value;
+          }
+        } else {
+          lhsBuilder_.mergeFrom(value);
+        }
+        bitField0_ |= 0x00000001;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      public Builder clearLhs() {
+        bitField0_ = (bitField0_ & ~0x00000001);
+        lhs_ = null;
+        if (lhsBuilder_ != null) {
+          lhsBuilder_.dispose();
+          lhsBuilder_ = null;
+        }
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      public io.littlehorse.sdk.common.proto.VariableAssignment.Builder getLhsBuilder() {
+        bitField0_ |= 0x00000001;
+        onChanged();
+        return getLhsFieldBuilder().getBuilder();
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      public io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder getLhsOrBuilder() {
+        if (lhsBuilder_ != null) {
+          return lhsBuilder_.getMessageOrBuilder();
+        } else {
+          return lhs_ == null ?
+              io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : lhs_;
+        }
+      }
+      /**
+       * <pre>
+       * The left-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment lhs = 1;</code>
+       */
+      private com.google.protobuf.SingleFieldBuilderV3<
+          io.littlehorse.sdk.common.proto.VariableAssignment, io.littlehorse.sdk.common.proto.VariableAssignment.Builder, io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder> 
+          getLhsFieldBuilder() {
+        if (lhsBuilder_ == null) {
+          lhsBuilder_ = new com.google.protobuf.SingleFieldBuilderV3<
+              io.littlehorse.sdk.common.proto.VariableAssignment, io.littlehorse.sdk.common.proto.VariableAssignment.Builder, io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder>(
+                  getLhs(),
+                  getParentForChildren(),
+                  isClean());
+          lhs_ = null;
+        }
+        return lhsBuilder_;
+      }
+
+      private int operation_ = 0;
+      /**
+       * <pre>
+       * The operator in the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableMutationType operation = 2;</code>
+       * @return The enum numeric value on the wire for operation.
+       */
+      @java.lang.Override public int getOperationValue() {
+        return operation_;
+      }
+      /**
+       * <pre>
+       * The operator in the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableMutationType operation = 2;</code>
+       * @param value The enum numeric value on the wire for operation to set.
+       * @return This builder for chaining.
+       */
+      public Builder setOperationValue(int value) {
+        operation_ = value;
+        bitField0_ |= 0x00000002;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The operator in the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableMutationType operation = 2;</code>
+       * @return The operation.
+       */
+      @java.lang.Override
+      public io.littlehorse.sdk.common.proto.VariableMutationType getOperation() {
+        io.littlehorse.sdk.common.proto.VariableMutationType result = io.littlehorse.sdk.common.proto.VariableMutationType.forNumber(operation_);
+        return result == null ? io.littlehorse.sdk.common.proto.VariableMutationType.UNRECOGNIZED : result;
+      }
+      /**
+       * <pre>
+       * The operator in the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableMutationType operation = 2;</code>
+       * @param value The operation to set.
+       * @return This builder for chaining.
+       */
+      public Builder setOperation(io.littlehorse.sdk.common.proto.VariableMutationType value) {
+        if (value == null) {
+          throw new NullPointerException();
+        }
+        bitField0_ |= 0x00000002;
+        operation_ = value.getNumber();
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The operator in the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableMutationType operation = 2;</code>
+       * @return This builder for chaining.
+       */
+      public Builder clearOperation() {
+        bitField0_ = (bitField0_ & ~0x00000002);
+        operation_ = 0;
+        onChanged();
+        return this;
+      }
+
+      private io.littlehorse.sdk.common.proto.VariableAssignment rhs_;
+      private com.google.protobuf.SingleFieldBuilderV3<
+          io.littlehorse.sdk.common.proto.VariableAssignment, io.littlehorse.sdk.common.proto.VariableAssignment.Builder, io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder> rhsBuilder_;
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       * @return Whether the rhs field is set.
+       */
+      public boolean hasRhs() {
+        return ((bitField0_ & 0x00000004) != 0);
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       * @return The rhs.
+       */
+      public io.littlehorse.sdk.common.proto.VariableAssignment getRhs() {
+        if (rhsBuilder_ == null) {
+          return rhs_ == null ? io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : rhs_;
+        } else {
+          return rhsBuilder_.getMessage();
+        }
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      public Builder setRhs(io.littlehorse.sdk.common.proto.VariableAssignment value) {
+        if (rhsBuilder_ == null) {
+          if (value == null) {
+            throw new NullPointerException();
+          }
+          rhs_ = value;
+        } else {
+          rhsBuilder_.setMessage(value);
+        }
+        bitField0_ |= 0x00000004;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      public Builder setRhs(
+          io.littlehorse.sdk.common.proto.VariableAssignment.Builder builderForValue) {
+        if (rhsBuilder_ == null) {
+          rhs_ = builderForValue.build();
+        } else {
+          rhsBuilder_.setMessage(builderForValue.build());
+        }
+        bitField0_ |= 0x00000004;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      public Builder mergeRhs(io.littlehorse.sdk.common.proto.VariableAssignment value) {
+        if (rhsBuilder_ == null) {
+          if (((bitField0_ & 0x00000004) != 0) &&
+            rhs_ != null &&
+            rhs_ != io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance()) {
+            getRhsBuilder().mergeFrom(value);
+          } else {
+            rhs_ = value;
+          }
+        } else {
+          rhsBuilder_.mergeFrom(value);
+        }
+        bitField0_ |= 0x00000004;
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      public Builder clearRhs() {
+        bitField0_ = (bitField0_ & ~0x00000004);
+        rhs_ = null;
+        if (rhsBuilder_ != null) {
+          rhsBuilder_.dispose();
+          rhsBuilder_ = null;
+        }
+        onChanged();
+        return this;
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      public io.littlehorse.sdk.common.proto.VariableAssignment.Builder getRhsBuilder() {
+        bitField0_ |= 0x00000004;
+        onChanged();
+        return getRhsFieldBuilder().getBuilder();
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      public io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder getRhsOrBuilder() {
+        if (rhsBuilder_ != null) {
+          return rhsBuilder_.getMessageOrBuilder();
+        } else {
+          return rhs_ == null ?
+              io.littlehorse.sdk.common.proto.VariableAssignment.getDefaultInstance() : rhs_;
+        }
+      }
+      /**
+       * <pre>
+       * The right-hand-side of the expression.
+       * </pre>
+       *
+       * <code>.littlehorse.VariableAssignment rhs = 3;</code>
+       */
+      private com.google.protobuf.SingleFieldBuilderV3<
+          io.littlehorse.sdk.common.proto.VariableAssignment, io.littlehorse.sdk.common.proto.VariableAssignment.Builder, io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder> 
+          getRhsFieldBuilder() {
+        if (rhsBuilder_ == null) {
+          rhsBuilder_ = new com.google.protobuf.SingleFieldBuilderV3<
+              io.littlehorse.sdk.common.proto.VariableAssignment, io.littlehorse.sdk.common.proto.VariableAssignment.Builder, io.littlehorse.sdk.common.proto.VariableAssignmentOrBuilder>(
+                  getRhs(),
+                  getParentForChildren(),
+                  isClean());
+          rhs_ = null;
+        }
+        return rhsBuilder_;
+      }
+      @java.lang.Override
+      public final Builder setUnknownFields(
+          final com.google.protobuf.UnknownFieldSet unknownFields) {
+        return super.setUnknownFields(unknownFields);
+      }
+
+      @java.lang.Override
+      public final Builder mergeUnknownFields(
+          final com.google.protobuf.UnknownFieldSet unknownFields) {
+        return super.mergeUnknownFields(unknownFields);
+      }
+
+
+      // @@protoc_insertion_point(builder_scope:littlehorse.VariableAssignment.Expression)
+    }
+
+    // @@protoc_insertion_point(class_scope:littlehorse.VariableAssignment.Expression)
+    private static final io.littlehorse.sdk.common.proto.VariableAssignment.Expression DEFAULT_INSTANCE;
+    static {
+      DEFAULT_INSTANCE = new io.littlehorse.sdk.common.proto.VariableAssignment.Expression();
+    }
+
+    public static io.littlehorse.sdk.common.proto.VariableAssignment.Expression getDefaultInstance() {
+      return DEFAULT_INSTANCE;
+    }
+
+    private static final com.google.protobuf.Parser<Expression>
+        PARSER = new com.google.protobuf.AbstractParser<Expression>() {
+      @java.lang.Override
+      public Expression parsePartialFrom(
+          com.google.protobuf.CodedInputStream input,
+          com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+          throws com.google.protobuf.InvalidProtocolBufferException {
+        Builder builder = newBuilder();
+        try {
+          builder.mergeFrom(input, extensionRegistry);
+        } catch (com.google.protobuf.InvalidProtocolBufferException e) {
+          throw e.setUnfinishedMessage(builder.buildPartial());
+        } catch (com.google.protobuf.UninitializedMessageException e) {
+          throw e.asInvalidProtocolBufferException().setUnfinishedMessage(builder.buildPartial());
+        } catch (java.io.IOException e) {
+          throw new com.google.protobuf.InvalidProtocolBufferException(e)
+              .setUnfinishedMessage(builder.buildPartial());
+        }
+        return builder.buildPartial();
+      }
+    };
+
+    public static com.google.protobuf.Parser<Expression> parser() {
+      return PARSER;
+    }
+
+    @java.lang.Override
+    public com.google.protobuf.Parser<Expression> getParserForType() {
+      return PARSER;
+    }
+
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignment.Expression getDefaultInstanceForType() {
+      return DEFAULT_INSTANCE;
+    }
+
+  }
+
   private int bitField0_;
   private int sourceCase_ = 0;
   @SuppressWarnings("serial")
@@ -1835,6 +2900,7 @@ public enum SourceCase
     LITERAL_VALUE(3),
     FORMAT_STRING(4),
     NODE_OUTPUT(5),
+    EXPRESSION(6),
     SOURCE_NOT_SET(0);
     private final int value;
     private SourceCase(int value) {
@@ -1856,6 +2922,7 @@ public static SourceCase forNumber(int value) {
         case 3: return LITERAL_VALUE;
         case 4: return FORMAT_STRING;
         case 5: return NODE_OUTPUT;
+        case 6: return EXPRESSION;
         case 0: return SOURCE_NOT_SET;
         default: return null;
       }
@@ -2129,6 +3196,49 @@ public io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReferenceOrB
     return io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReference.getDefaultInstance();
   }
 
+  public static final int EXPRESSION_FIELD_NUMBER = 6;
+  /**
+   * <pre>
+   * Assign the value of an Expression.
+   * </pre>
+   *
+   * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+   * @return Whether the expression field is set.
+   */
+  @java.lang.Override
+  public boolean hasExpression() {
+    return sourceCase_ == 6;
+  }
+  /**
+   * <pre>
+   * Assign the value of an Expression.
+   * </pre>
+   *
+   * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+   * @return The expression.
+   */
+  @java.lang.Override
+  public io.littlehorse.sdk.common.proto.VariableAssignment.Expression getExpression() {
+    if (sourceCase_ == 6) {
+       return (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_;
+    }
+    return io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+  }
+  /**
+   * <pre>
+   * Assign the value of an Expression.
+   * </pre>
+   *
+   * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+   */
+  @java.lang.Override
+  public io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder getExpressionOrBuilder() {
+    if (sourceCase_ == 6) {
+       return (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_;
+    }
+    return io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+  }
+
   private byte memoizedIsInitialized = -1;
   @java.lang.Override
   public final boolean isInitialized() {
@@ -2158,6 +3268,9 @@ public void writeTo(com.google.protobuf.CodedOutputStream output)
     if (sourceCase_ == 5) {
       output.writeMessage(5, (io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReference) source_);
     }
+    if (sourceCase_ == 6) {
+      output.writeMessage(6, (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_);
+    }
     getUnknownFields().writeTo(output);
   }
 
@@ -2185,6 +3298,10 @@ public int getSerializedSize() {
       size += com.google.protobuf.CodedOutputStream
         .computeMessageSize(5, (io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReference) source_);
     }
+    if (sourceCase_ == 6) {
+      size += com.google.protobuf.CodedOutputStream
+        .computeMessageSize(6, (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_);
+    }
     size += getUnknownFields().getSerializedSize();
     memoizedSize = size;
     return size;
@@ -2223,6 +3340,10 @@ public boolean equals(final java.lang.Object obj) {
         if (!getNodeOutput()
             .equals(other.getNodeOutput())) return false;
         break;
+      case 6:
+        if (!getExpression()
+            .equals(other.getExpression())) return false;
+        break;
       case 0:
       default:
     }
@@ -2258,6 +3379,10 @@ public int hashCode() {
         hash = (37 * hash) + NODE_OUTPUT_FIELD_NUMBER;
         hash = (53 * hash) + getNodeOutput().hashCode();
         break;
+      case 6:
+        hash = (37 * hash) + EXPRESSION_FIELD_NUMBER;
+        hash = (53 * hash) + getExpression().hashCode();
+        break;
       case 0:
       default:
     }
@@ -2412,6 +3537,9 @@ public Builder clear() {
       if (nodeOutputBuilder_ != null) {
         nodeOutputBuilder_.clear();
       }
+      if (expressionBuilder_ != null) {
+        expressionBuilder_.clear();
+      }
       sourceCase_ = 0;
       source_ = null;
       return this;
@@ -2471,6 +3599,10 @@ private void buildPartialOneofs(io.littlehorse.sdk.common.proto.VariableAssignme
           nodeOutputBuilder_ != null) {
         result.source_ = nodeOutputBuilder_.build();
       }
+      if (sourceCase_ == 6 &&
+          expressionBuilder_ != null) {
+        result.source_ = expressionBuilder_.build();
+      }
     }
 
     @java.lang.Override
@@ -2541,6 +3673,10 @@ public Builder mergeFrom(io.littlehorse.sdk.common.proto.VariableAssignment othe
           mergeNodeOutput(other.getNodeOutput());
           break;
         }
+        case EXPRESSION: {
+          mergeExpression(other.getExpression());
+          break;
+        }
         case SOURCE_NOT_SET: {
           break;
         }
@@ -2603,6 +3739,13 @@ public Builder mergeFrom(
               sourceCase_ = 5;
               break;
             } // case 42
+            case 50: {
+              input.readMessage(
+                  getExpressionFieldBuilder().getBuilder(),
+                  extensionRegistry);
+              sourceCase_ = 6;
+              break;
+            } // case 50
             default: {
               if (!super.parseUnknownField(input, extensionRegistry, tag)) {
                 done = true; // was an endgroup tag
@@ -3400,6 +4543,184 @@ public io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReferenceOrB
       onChanged();
       return nodeOutputBuilder_;
     }
+
+    private com.google.protobuf.SingleFieldBuilderV3<
+        io.littlehorse.sdk.common.proto.VariableAssignment.Expression, io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder, io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder> expressionBuilder_;
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     * @return Whether the expression field is set.
+     */
+    @java.lang.Override
+    public boolean hasExpression() {
+      return sourceCase_ == 6;
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     * @return The expression.
+     */
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignment.Expression getExpression() {
+      if (expressionBuilder_ == null) {
+        if (sourceCase_ == 6) {
+          return (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_;
+        }
+        return io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+      } else {
+        if (sourceCase_ == 6) {
+          return expressionBuilder_.getMessage();
+        }
+        return io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+      }
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    public Builder setExpression(io.littlehorse.sdk.common.proto.VariableAssignment.Expression value) {
+      if (expressionBuilder_ == null) {
+        if (value == null) {
+          throw new NullPointerException();
+        }
+        source_ = value;
+        onChanged();
+      } else {
+        expressionBuilder_.setMessage(value);
+      }
+      sourceCase_ = 6;
+      return this;
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    public Builder setExpression(
+        io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder builderForValue) {
+      if (expressionBuilder_ == null) {
+        source_ = builderForValue.build();
+        onChanged();
+      } else {
+        expressionBuilder_.setMessage(builderForValue.build());
+      }
+      sourceCase_ = 6;
+      return this;
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    public Builder mergeExpression(io.littlehorse.sdk.common.proto.VariableAssignment.Expression value) {
+      if (expressionBuilder_ == null) {
+        if (sourceCase_ == 6 &&
+            source_ != io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance()) {
+          source_ = io.littlehorse.sdk.common.proto.VariableAssignment.Expression.newBuilder((io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_)
+              .mergeFrom(value).buildPartial();
+        } else {
+          source_ = value;
+        }
+        onChanged();
+      } else {
+        if (sourceCase_ == 6) {
+          expressionBuilder_.mergeFrom(value);
+        } else {
+          expressionBuilder_.setMessage(value);
+        }
+      }
+      sourceCase_ = 6;
+      return this;
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    public Builder clearExpression() {
+      if (expressionBuilder_ == null) {
+        if (sourceCase_ == 6) {
+          sourceCase_ = 0;
+          source_ = null;
+          onChanged();
+        }
+      } else {
+        if (sourceCase_ == 6) {
+          sourceCase_ = 0;
+          source_ = null;
+        }
+        expressionBuilder_.clear();
+      }
+      return this;
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    public io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder getExpressionBuilder() {
+      return getExpressionFieldBuilder().getBuilder();
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    @java.lang.Override
+    public io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder getExpressionOrBuilder() {
+      if ((sourceCase_ == 6) && (expressionBuilder_ != null)) {
+        return expressionBuilder_.getMessageOrBuilder();
+      } else {
+        if (sourceCase_ == 6) {
+          return (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_;
+        }
+        return io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+      }
+    }
+    /**
+     * <pre>
+     * Assign the value of an Expression.
+     * </pre>
+     *
+     * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+     */
+    private com.google.protobuf.SingleFieldBuilderV3<
+        io.littlehorse.sdk.common.proto.VariableAssignment.Expression, io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder, io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder> 
+        getExpressionFieldBuilder() {
+      if (expressionBuilder_ == null) {
+        if (!(sourceCase_ == 6)) {
+          source_ = io.littlehorse.sdk.common.proto.VariableAssignment.Expression.getDefaultInstance();
+        }
+        expressionBuilder_ = new com.google.protobuf.SingleFieldBuilderV3<
+            io.littlehorse.sdk.common.proto.VariableAssignment.Expression, io.littlehorse.sdk.common.proto.VariableAssignment.Expression.Builder, io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder>(
+                (io.littlehorse.sdk.common.proto.VariableAssignment.Expression) source_,
+                getParentForChildren(),
+                isClean());
+        source_ = null;
+      }
+      sourceCase_ = 6;
+      onChanged();
+      return expressionBuilder_;
+    }
     @java.lang.Override
     public final Builder setUnknownFields(
         final com.google.protobuf.UnknownFieldSet unknownFields) {
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignmentOrBuilder.java b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignmentOrBuilder.java
index eedb5a8af..a7b17eee3 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignmentOrBuilder.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/common/proto/VariableAssignmentOrBuilder.java
@@ -152,5 +152,32 @@ public interface VariableAssignmentOrBuilder extends
    */
   io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReferenceOrBuilder getNodeOutputOrBuilder();
 
+  /**
+   * <pre>
+   * Assign the value of an Expression.
+   * </pre>
+   *
+   * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+   * @return Whether the expression field is set.
+   */
+  boolean hasExpression();
+  /**
+   * <pre>
+   * Assign the value of an Expression.
+   * </pre>
+   *
+   * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+   * @return The expression.
+   */
+  io.littlehorse.sdk.common.proto.VariableAssignment.Expression getExpression();
+  /**
+   * <pre>
+   * Assign the value of an Expression.
+   * </pre>
+   *
+   * <code>.littlehorse.VariableAssignment.Expression expression = 6;</code>
+   */
+  io.littlehorse.sdk.common.proto.VariableAssignment.ExpressionOrBuilder getExpressionOrBuilder();
+
   io.littlehorse.sdk.common.proto.VariableAssignment.SourceCase getSourceCase();
 }
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/LHExpression.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/LHExpression.java
new file mode 100644
index 000000000..e143bc8f9
--- /dev/null
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/LHExpression.java
@@ -0,0 +1,83 @@
+package io.littlehorse.sdk.wfsdk;
+
+import java.io.Serializable;
+
+public interface LHExpression extends Serializable {
+
+    /**
+     * Returns an expression whose value is the `other` added to this expression.
+     * @param other the value to be added to this expression.
+     * @return an expression whose value is the `other` added to this expression.
+     */
+    LHExpression add(Serializable other);
+
+    /**
+     * Returns an expression whose value is the `other` subtracted from this expression.
+     * @param other the value to be subtracted from this expression.
+     * @return an expression whose value is the `other` subtracted from this expression.
+     */
+    LHExpression subtract(Serializable other);
+
+    /**
+     * Returns an expression whose value is the `other` multiplied by this expression.
+     * @param other the value to be multiplied by this expression.
+     * @return an expression whose value is the `other` multiplied by this expression.
+     */
+    LHExpression multiply(Serializable other);
+
+    /**
+     * Returns an expression whose value is this expression divided by the `other`.
+     * @param other the value to divide this expression by.
+     * @return an expression whose value is this expression divided by the `other`.
+     */
+    LHExpression divide(Serializable other);
+
+    /**
+     * Returns an expression whose value is this expression extended by the `other`.
+     * @param other the value to extend this expression by.
+     * @return an expression whose value is this expression extended by the `other`.
+     */
+    LHExpression extend(Serializable other);
+
+    /**
+     * Returns an expression whose value is this expression with all occurrences of
+     * `other` removed.
+     * @param other the value to remove from this expression.
+     * @return an expression whose value is this expression with all occurrences of
+     * `other` removed.
+     */
+    LHExpression removeIfPresent(Serializable other);
+
+    /**
+     * Returns an expression whose value is this expression with the index specified
+     * by `other` removed.
+     *
+     * Valid only for JSON_ARR expressions.
+     * @param index the index at which to insert the `other`.
+     * @return an expression whose value is this expression with the `other` inserted
+     * at the specified `index`.
+     */
+    LHExpression removeIndex(int index);
+
+    /**
+     * Returns an expression whose value is this expression with the index specified
+     * by `index` removed.
+     *
+     * Valid only for JSON_ARR expressions.
+     * @param index the index at which to remove the value.
+     * @return an expression whose value is this expression with the value at the
+     * specified `index` removed.
+     */
+    LHExpression removeIndex(LHExpression index);
+
+    /**
+     * Returns an expression whose value is this expression with the key specified
+     * by `key` removed.
+     *
+     * Valid only for JSON_OBJ expressions.
+     * @param key the key to remove from this expression.
+     * @return an expression whose value is this expression with the key specified
+     * by `key` removed.
+     */
+    LHExpression removeKey(Serializable key);
+}
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/NodeOutput.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/NodeOutput.java
index 81cc76810..ddb1ea51b 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/NodeOutput.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/NodeOutput.java
@@ -1,12 +1,10 @@
 package io.littlehorse.sdk.wfsdk;
 
-import java.io.Serializable;
-
 /**
  * `NodeOutput` represents the output of a Node execution. It can be used to set a timeout on a
  * node, or as input for a Variable Mutation.
  */
-public interface NodeOutput extends Serializable {
+public interface NodeOutput extends LHExpression {
     /**
      * Valid only for output of the JSON_OBJ or JSON_ARR types. Returns a new NodeOutput handle
      * which points to Json element referred to by the json path.
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WfRunVariable.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WfRunVariable.java
index b59f8f19a..a5a1002a5 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WfRunVariable.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WfRunVariable.java
@@ -5,7 +5,7 @@
 import java.io.Serializable;
 
 /** A WfRunVariable is a handle on a Variable in a WfSpec. */
-public interface WfRunVariable extends Serializable {
+public interface WfRunVariable extends LHExpression {
     /**
      * Valid only for output of the JSON_OBJ or JSON_ARR types. Returns a new WfRunVariable handle
      * which points to Json element referred to by the json path.
@@ -79,4 +79,140 @@ public interface WfRunVariable extends Serializable {
      * @return this WfRunVariable.
      */
     WfRunVariable masked();
+
+    /**
+     * Sets the default value for this WfRunVariable.
+     * @param defaultVal is the default value for this variable.
+     * @return this WfRunVariable.
+     */
+    WfRunVariable withDefault(Object defaultVal);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if this WfRunVariable is LESS_THAN the provided rhs.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.LESS_THAN, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is LESS_THAN the provided rhs.
+     */
+    WorkflowCondition isLessThan(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if this WfRunVariable is LESS_THAN_EQU the provided rhs.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.LESS_THAN_EQ, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is LESS_THAN_EQ the provided rhs.
+     */
+    WorkflowCondition isLessThanEq(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if this WfRunVariable is GREATER_THAN_EQ the provided rhs.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.GREATER_THAN_EQ, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is GREATER_THAN_EQ the provided rhs.
+     */
+    WorkflowCondition isGreaterThanEq(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if this WfRunVariable is GREATER_THAN the provided rhs.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.GREATER_THAN, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is GREATER_THAN the provided rhs.
+     */
+    WorkflowCondition isGreaterThan(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if this WfRunVariable is EQUALS to the provided rhs.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.EQUALS, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is GREATER_THAN the provided rhs.
+     */
+    WorkflowCondition isEqualTo(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if this WfRunVariable is NOT_EQUALS to the provided rhs.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.EQUALS, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is GREATER_THAN the provided rhs.
+     */
+    WorkflowCondition isNotEqualTo(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if the RHS is contained inside this variable. For JSON_OBJ, returns
+     * true if the RHS is a key. For JSON_ARR, returns true if the RHS is equal to one of the
+     * elements in the array.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.BETWEEN, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is BETWEEN the provided rhs.
+     */
+    WorkflowCondition doesContain(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if the RHS is not contained inside this variable. For JSON_OBJ, returns
+     * true if the RHS is not a key. For JSON_ARR, returns true if the RHS is not equal to any of
+     * the elements in the array.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.NOT_BETWEEN, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is NOT_BETWEEN the provided rhs.
+     */
+    WorkflowCondition doesNotContain(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if the value of this WfRunVariable is contained in the provided RHS.
+     * For an RHS of type JSON_OBJ, returns true if the RHS contains a key that is equal to the
+     * value of this WfRunVariable. For an RHS of type JSON_ARR, returns true if the RHS contains
+     * an element that is equal to the value of this WfRunVariable.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.BETWEEN, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is BETWEEN the provided rhs.
+     */
+    WorkflowCondition isIn(Serializable rhs);
+
+    /**
+     * Returns a WorkflowCondition (treated like a boolean in the WfSpec control flow logic) that
+     * evaluates to true if the value of this WfRunVariable is not contained in the provided RHS.
+     * For an RHS of type JSON_OBJ, returns true if the RHS does not contain a key that is equal
+     * to the value of this WfRunVariable. For an RHS of type JSON_ARR, returns true if the RHS does
+     * not contain an element that is equal to the value of this WfRunVariable.
+     *
+     * Equivalent to WorkflowThread#condition(this, Comparator.NOT_BETWEEN, rhs);
+     *
+     * @param rhs is the RHS to compare this WfRunVariable to.
+     * @return true if this WfRunVariable is NOT_BETWEEN the provided rhs.
+     */
+    WorkflowCondition isNotIn(Serializable rhs);
+
+    /**
+     * Mutates the value of this WfRunVariable and sets it to the the value provided on the RHS.
+     *
+     * If the LHS of this WfRunVariable is set, then the sub-element of this WfRunVariable
+     * provided by the Json Path is mutated.
+     * @param rhs is the value to set this WfRunVariable to.
+     */
+    void assignTo(Serializable rhs);
 }
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WorkflowThread.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WorkflowThread.java
index c0ffac4de..07701fa3b 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WorkflowThread.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/WorkflowThread.java
@@ -109,6 +109,55 @@ public interface WorkflowThread {
      */
     LHFormatString format(String format, WfRunVariable... args);
 
+    /**
+     * Creates a variable of type INT in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareInt(String name);
+
+    /**
+     * Creates a variable of type STR in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareStr(String name);
+
+    /**
+     * Creates a variable of type DOUBLE in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareDouble(String name);
+
+    /**
+     * Creates a variable of type BYTES in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareBytes(String name);
+
+    /**
+     * Creates a variable of type JSON_ARR in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareJsonArr(String name);
+
+    /**
+     * Creates a variable of type JSON_OBJ in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareJsonObj(String name);
+
+    /**
+     * Creates a variable of type BOOL in the ThreadSpec.
+     * @param name is the name of the variable.
+     * @return a WfRunVariable.
+     */
+    WfRunVariable declareBool(String name);
+
     /**
      * Defines a Variable in the `ThreadSpec` and returns a handle to it.
      *
@@ -365,8 +414,8 @@ void scheduleReminderTaskOnAssignment(
     void handleAnyFailure(NodeOutput node, ThreadFunc handler);
 
     /**
-     * Returns a WorkflowCondition that can be used in `ThreadBuilder::doIf()` or
-     * `ThreadBuilder::doElse()`.
+     * Returns a WorkflowCondition that can be used in `WorkflowThread::doIf()` or
+     * `WorkflowThread::doIfElse()`.
      *
      * @param lhs is either a literal value (which the Library casts to a Variable Value) or a
      *     `WfRunVariable` representing the LHS of the expression.
@@ -421,4 +470,86 @@ void scheduleReminderTaskOnAssignment(
      */
     SpawnedThreads spawnThreadForEach(
             WfRunVariable arrVar, String threadName, ThreadFunc threadFunc, Map<String, Object> inputVars);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * expression is given by multiplying the left hand with the right hand. This method does not result
+     * in any modifications being made to a variable; it only returns a value calculated inline.
+     * @param lhs is the left hand side of the expression.
+     * @param rhs is the right hand side of the expression, which is multiplied against the lhs.
+     * @return an LHExpression representing the result of the multiplication.
+     */
+    LHExpression multiply(Serializable lhs, Serializable rhs);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * expression is given by adding the left hand with the right hand. This method does not result
+     * in any modifications being made to a variable; it only returns a value calculated inline.
+     *
+     * If the LHS is a DOUBLE or INT, mathematical addition is used. If the LHS is a JSON_ARR, the
+     * RHS is added as a single element at the end of the array.
+     * @param lhs is the left hand side of the expression.
+     * @param rhs is the right hand side of the expression, which is added to the lhs.
+     * @return an LHExpression representing the result of the addition.
+     */
+    LHExpression add(Serializable lhs, Serializable rhs);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * expression is given by dividing the left hand by the right hand. This method does not result
+     * in any modifications being made to a variable; it only returns a value calculated inline.
+     * @param lhs is the left hand side of the expression.
+     * @param rhs is the right hand side of the expression, which is divided into the lhs.
+     * @return an LHExpression representing the result of the division.
+     */
+    LHExpression divide(Serializable lhs, Serializable rhs);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * expression is given by subtracting the right hand from the left hand. This method does not result
+     * in any modifications being made to a variable; it only returns a value calculated inline.
+     * @param lhs is the left hand side of the expression.
+     * @param rhs is the right hand side of the expression, which is divided into the lhs.
+     * @return an LHExpression representing the result of the division.
+     */
+    LHExpression subtract(Serializable lhs, Serializable rhs);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * expression is given by extending the left-hand-side with the right-hand-side. It is valid for
+     * LHS of type STR or JSON_ARR, and results in concatenating both together.
+     * @param lhs is the left hand side of the expression.
+     * @param rhs is the right hand side of the expression, which is concatenated with the lhs.
+     * @return an LHExpression representing the result of the concatenation.
+     */
+    LHExpression extend(Serializable lhs, Serializable rhs);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * result is formed by removing all occurrences from RHS from the LHS. Valid only for LHS of type
+     * JSON_ARR.
+     * @param lhs is the left hand side of the expression.
+     * @param rhs is the right hand side of the expression, which is removed from the lhs.
+     * @return an LHExpression representing the result of the removal.
+     */
+    LHExpression removeIfPresent(Serializable lhs, Serializable rhs);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * result is formed by removing all occurrences from RHS from the LHS. Valid only for LHS of type
+     * JSON_ARR.
+     * @param lhs is the left hand side of the expression.
+     * @param index is the right hand side of the expression, which is removed from the lhs.
+     * @return an LHExpression representing the result of the removal.
+     */
+    LHExpression removeIndex(Serializable lhs, Serializable index);
+
+    /**
+     * Returns an expression that can be passed into a variable assignment/mutation or a TaskRun. The
+     * result is formed by removing the RHS key from the LHS. Valid only for LHS of type JSON_OBJ.
+     * @param lhs is the left hand side of the expression.
+     * @param key is the right hand side of the expression, which is removed from the lhs.
+     * @return an LHExpression representing the result of the removal.
+     */
+    LHExpression removeKey(Serializable lhs, Serializable key);
 }
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/BuilderUtil.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/BuilderUtil.java
index a8a044c94..32c67e72a 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/BuilderUtil.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/BuilderUtil.java
@@ -3,6 +3,7 @@
 import io.littlehorse.sdk.common.LHLibUtil;
 import io.littlehorse.sdk.common.exception.LHSerdeError;
 import io.littlehorse.sdk.common.proto.VariableAssignment;
+import io.littlehorse.sdk.common.proto.VariableAssignment.Expression;
 import io.littlehorse.sdk.common.proto.VariableAssignment.NodeOutputReference;
 import io.littlehorse.sdk.common.proto.VariableValue;
 
@@ -32,6 +33,12 @@ static VariableAssignment assignVariable(Object variable) {
                     .setFormat(assignVariable(format.getFormat()))
                     .addAllArgs(format.getArgs()));
 
+        } else if (variable instanceof LHExpressionImpl) {
+            LHExpressionImpl expr = (LHExpressionImpl) variable;
+            builder.setExpression(Expression.newBuilder()
+                    .setLhs(assignVariable(expr.getLhs()))
+                    .setOperation(expr.getOperation())
+                    .setRhs(assignVariable(expr.getRhs())));
         } else {
             try {
                 VariableValue defVal = LHLibUtil.objToVarVal(variable);
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/LHExpressionImpl.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/LHExpressionImpl.java
new file mode 100644
index 000000000..956a619ca
--- /dev/null
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/LHExpressionImpl.java
@@ -0,0 +1,65 @@
+package io.littlehorse.sdk.wfsdk.internal;
+
+import io.littlehorse.sdk.common.proto.VariableMutationType;
+import io.littlehorse.sdk.wfsdk.LHExpression;
+import java.io.Serializable;
+import lombok.Getter;
+
+@Getter
+public class LHExpressionImpl implements LHExpression {
+
+    private Serializable lhs;
+    private Serializable rhs;
+    private VariableMutationType operation;
+
+    public LHExpressionImpl(Serializable lhs, VariableMutationType operation, Serializable rhs) {
+        this.lhs = lhs;
+        this.rhs = rhs;
+        this.operation = operation;
+    }
+
+    @Override
+    public LHExpression add(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.ADD, other);
+    }
+
+    @Override
+    public LHExpression subtract(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.SUBTRACT, other);
+    }
+
+    @Override
+    public LHExpression multiply(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.MULTIPLY, other);
+    }
+
+    @Override
+    public LHExpression divide(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.DIVIDE, other);
+    }
+
+    @Override
+    public LHExpression extend(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.EXTEND, other);
+    }
+
+    @Override
+    public LHExpression removeIfPresent(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_IF_PRESENT, other);
+    }
+
+    @Override
+    public LHExpression removeIndex(int index) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeIndex(LHExpression index) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeKey(Serializable key) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_KEY, key);
+    }
+}
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/NodeOutputImpl.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/NodeOutputImpl.java
index 173458264..4bcd4db7e 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/NodeOutputImpl.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/NodeOutputImpl.java
@@ -1,6 +1,9 @@
 package io.littlehorse.sdk.wfsdk.internal;
 
+import io.littlehorse.sdk.common.proto.VariableMutationType;
+import io.littlehorse.sdk.wfsdk.LHExpression;
 import io.littlehorse.sdk.wfsdk.NodeOutput;
+import java.io.Serializable;
 
 class NodeOutputImpl implements NodeOutput {
 
@@ -26,4 +29,49 @@ public NodeOutputImpl timeout(int timeoutSeconds) {
         parent.addTimeoutToExtEvt(this, timeoutSeconds);
         return this;
     }
+
+    @Override
+    public LHExpression add(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.ADD, other);
+    }
+
+    @Override
+    public LHExpression subtract(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.SUBTRACT, other);
+    }
+
+    @Override
+    public LHExpression multiply(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.MULTIPLY, other);
+    }
+
+    @Override
+    public LHExpression divide(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.DIVIDE, other);
+    }
+
+    @Override
+    public LHExpression extend(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.EXTEND, other);
+    }
+
+    @Override
+    public LHExpression removeIfPresent(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_IF_PRESENT, other);
+    }
+
+    @Override
+    public LHExpression removeIndex(int index) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeIndex(LHExpression index) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeKey(Serializable key) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_KEY, key);
+    }
 }
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImpl.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImpl.java
index b982d1e53..48f6bd5ec 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImpl.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImpl.java
@@ -3,13 +3,17 @@
 import io.littlehorse.sdk.common.LHLibUtil;
 import io.littlehorse.sdk.common.exception.LHMisconfigurationException;
 import io.littlehorse.sdk.common.exception.LHSerdeError;
+import io.littlehorse.sdk.common.proto.Comparator;
 import io.littlehorse.sdk.common.proto.JsonIndex;
 import io.littlehorse.sdk.common.proto.ThreadVarDef;
 import io.littlehorse.sdk.common.proto.VariableDef;
+import io.littlehorse.sdk.common.proto.VariableMutationType;
 import io.littlehorse.sdk.common.proto.VariableType;
 import io.littlehorse.sdk.common.proto.VariableValue;
 import io.littlehorse.sdk.common.proto.WfRunVariableAccessLevel;
+import io.littlehorse.sdk.wfsdk.LHExpression;
 import io.littlehorse.sdk.wfsdk.WfRunVariable;
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;
 import lombok.Getter;
@@ -29,9 +33,12 @@ class WfRunVariableImpl implements WfRunVariable {
 
     public String jsonPath;
 
-    public WfRunVariableImpl(String name, Object typeOrDefaultVal) {
+    private final WorkflowThreadImpl parent;
+
+    public WfRunVariableImpl(String name, Object typeOrDefaultVal, WorkflowThreadImpl parent) {
         this.name = name;
         this.typeOrDefaultVal = typeOrDefaultVal;
+        this.parent = parent;
 
         // As per GH Issue #582, the default is now PRIVATE_VAR.
         this.accessLevel = WfRunVariableAccessLevel.PRIVATE_VAR;
@@ -66,7 +73,7 @@ public WfRunVariableImpl jsonPath(String path) {
         if (!type.equals(VariableType.JSON_OBJ) && !type.equals(VariableType.JSON_ARR)) {
             throw new LHMisconfigurationException(String.format("JsonPath not allowed in a %s variable", type.name()));
         }
-        WfRunVariableImpl out = new WfRunVariableImpl(name, typeOrDefaultVal);
+        WfRunVariableImpl out = new WfRunVariableImpl(name, typeOrDefaultVal, parent);
         out.jsonPath = path;
         return out;
     }
@@ -89,6 +96,19 @@ public WfRunVariable required() {
         return this;
     }
 
+    @Override
+    public WfRunVariable withDefault(Object defaultVal) {
+        try {
+            VariableValue attempt = LHLibUtil.objToVarVal(defaultVal);
+            if (!LHLibUtil.fromValueCase(attempt.getValueCase()).equals(type)) {
+                throw new IllegalArgumentException("Default value type does not match variable type");
+            }
+        } catch (LHSerdeError e) {
+            throw new IllegalArgumentException("Was unable to convert provided default value to LH Variable Type", e);
+        }
+        return this;
+    }
+
     @Override
     public WfRunVariable searchableOn(String fieldPath, VariableType fieldType) {
         if (!fieldPath.startsWith("$.")) {
@@ -104,6 +124,106 @@ public WfRunVariable searchableOn(String fieldPath, VariableType fieldType) {
         return this;
     }
 
+    @Override
+    public WorkflowConditionImpl isEqualTo(Serializable rhs) {
+        return parent.condition(this, Comparator.EQUALS, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl isNotEqualTo(Serializable rhs) {
+        return parent.condition(this, Comparator.NOT_EQUALS, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl isGreaterThan(Serializable rhs) {
+        return parent.condition(this, Comparator.GREATER_THAN, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl isGreaterThanEq(Serializable rhs) {
+        return parent.condition(this, Comparator.GREATER_THAN_EQ, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl isLessThanEq(Serializable rhs) {
+        return parent.condition(this, Comparator.LESS_THAN_EQ, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl isLessThan(Serializable rhs) {
+        return parent.condition(this, Comparator.LESS_THAN, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl doesContain(Serializable rhs) {
+        return parent.condition(rhs, Comparator.IN, this);
+    }
+
+    @Override
+    public WorkflowConditionImpl doesNotContain(Serializable rhs) {
+        return parent.condition(rhs, Comparator.NOT_IN, this);
+    }
+
+    @Override
+    public WorkflowConditionImpl isIn(Serializable rhs) {
+        return parent.condition(this, Comparator.IN, rhs);
+    }
+
+    @Override
+    public WorkflowConditionImpl isNotIn(Serializable rhs) {
+        return parent.condition(this, Comparator.NOT_IN, rhs);
+    }
+
+    @Override
+    public void assignTo(Serializable rhs) {
+        parent.mutate(this, VariableMutationType.ASSIGN, rhs);
+    }
+
+    @Override
+    public LHExpression add(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.ADD, other);
+    }
+
+    @Override
+    public LHExpression subtract(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.SUBTRACT, other);
+    }
+
+    @Override
+    public LHExpression multiply(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.MULTIPLY, other);
+    }
+
+    @Override
+    public LHExpression divide(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.DIVIDE, other);
+    }
+
+    @Override
+    public LHExpression extend(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.EXTEND, other);
+    }
+
+    @Override
+    public LHExpression removeIfPresent(Serializable other) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_IF_PRESENT, other);
+    }
+
+    @Override
+    public LHExpression removeIndex(int index) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeIndex(LHExpression index) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeKey(Serializable key) {
+        return new LHExpressionImpl(this, VariableMutationType.REMOVE_KEY, key);
+    }
+
     public ThreadVarDef getSpec() {
         VariableDef.Builder varDef = VariableDef.newBuilder()
                 .setType(this.getType())
diff --git a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WorkflowThreadImpl.java b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WorkflowThreadImpl.java
index 1085d3f09..93a9f65de 100644
--- a/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WorkflowThreadImpl.java
+++ b/sdk-java/src/main/java/io/littlehorse/sdk/wfsdk/internal/WorkflowThreadImpl.java
@@ -41,6 +41,7 @@
 import io.littlehorse.sdk.common.proto.WaitForThreadsNode;
 import io.littlehorse.sdk.common.proto.WorkflowEventDefId;
 import io.littlehorse.sdk.wfsdk.IfElseBody;
+import io.littlehorse.sdk.wfsdk.LHExpression;
 import io.littlehorse.sdk.wfsdk.LHFormatString;
 import io.littlehorse.sdk.wfsdk.NodeOutput;
 import io.littlehorse.sdk.wfsdk.SpawnedThreads;
@@ -375,13 +376,89 @@ public void checkArgsVsTaskDef(List<VariableDef> taskDefInputVars, String taskDe
         }
     }
 
+    @Override
+    public LHExpression multiply(Serializable lhs, Serializable rhs) {
+        return new LHExpressionImpl(lhs, VariableMutationType.MULTIPLY, rhs);
+    }
+
+    @Override
+    public LHExpression add(Serializable lhs, Serializable rhs) {
+        return new LHExpressionImpl(lhs, VariableMutationType.ADD, rhs);
+    }
+
+    @Override
+    public LHExpression divide(Serializable lhs, Serializable rhs) {
+        return new LHExpressionImpl(lhs, VariableMutationType.DIVIDE, rhs);
+    }
+
+    @Override
+    public LHExpression subtract(Serializable lhs, Serializable rhs) {
+        return new LHExpressionImpl(lhs, VariableMutationType.SUBTRACT, rhs);
+    }
+
+    @Override
+    public LHExpression extend(Serializable lhs, Serializable rhs) {
+        return new LHExpressionImpl(lhs, VariableMutationType.EXTEND, rhs);
+    }
+
+    @Override
+    public LHExpression removeIfPresent(Serializable lhs, Serializable rhs) {
+        return new LHExpressionImpl(lhs, VariableMutationType.REMOVE_IF_PRESENT, rhs);
+    }
+
+    @Override
+    public LHExpression removeIndex(Serializable lhs, Serializable index) {
+        return new LHExpressionImpl(lhs, VariableMutationType.REMOVE_INDEX, index);
+    }
+
+    @Override
+    public LHExpression removeKey(Serializable lhs, Serializable key) {
+        return new LHExpressionImpl(lhs, VariableMutationType.REMOVE_KEY, key);
+    }
+
     public WfRunVariableImpl addVariable(String name, Object typeOrDefaultVal) {
         checkIfIsActive();
-        WfRunVariableImpl wfRunVariable = new WfRunVariableImpl(name, typeOrDefaultVal);
+        WfRunVariableImpl wfRunVariable = new WfRunVariableImpl(name, typeOrDefaultVal, this);
         wfRunVariables.add(wfRunVariable);
         return wfRunVariable;
     }
 
+    @Override
+    public WfRunVariable declareBool(String name) {
+        return addVariable(name, VariableType.BOOL);
+    }
+
+    @Override
+    public WfRunVariable declareInt(String name) {
+        return addVariable(name, VariableType.INT);
+    }
+
+    @Override
+    public WfRunVariable declareStr(String name) {
+        return addVariable(name, VariableType.STR);
+    }
+
+    @Override
+    public WfRunVariable declareDouble(String name) {
+        return addVariable(name, VariableType.DOUBLE);
+    }
+
+    @Override
+    public WfRunVariable declareBytes(String name) {
+        return addVariable(name, VariableType.BYTES);
+    }
+
+    @Override
+    public WfRunVariable declareJsonArr(String name) {
+        return addVariable(name, VariableType.JSON_ARR);
+    }
+
+    @Override
+    public WfRunVariable declareJsonObj(String name) {
+        return addVariable(name, VariableType.JSON_OBJ);
+    }
+
+    @Override
     public void doIf(WorkflowCondition condition, IfElseBody ifBody) {
         checkIfIsActive();
         WorkflowConditionImpl cond = (WorkflowConditionImpl) condition;
@@ -411,6 +488,7 @@ private void addNopNode() {
         addNode("nop", NodeCase.NOP, NopNode.newBuilder().build());
     }
 
+    @Override
     public void doIfElse(WorkflowCondition condition, IfElseBody ifBody, IfElseBody elseBody) {
         checkIfIsActive();
         WorkflowConditionImpl cond = (WorkflowConditionImpl) condition;
@@ -458,6 +536,7 @@ private List<VariableMutation> collectVariableMutations() {
         return variablesFromIfBlock;
     }
 
+    @Override
     public void doWhile(WorkflowCondition condition, ThreadFunc whileBody) {
         checkIfIsActive();
         WorkflowConditionImpl cond = (WorkflowConditionImpl) condition;
@@ -518,18 +597,21 @@ public SpawnedThreads spawnThreadForEach(
         return new SpawnedThreadsIterator(internalStartedThreadVar);
     }
 
+    @Override
     public void sleepSeconds(Object secondsToSleep) {
         checkIfIsActive();
         SleepNode.Builder n = SleepNode.newBuilder().setRawSeconds(assignVariable(secondsToSleep));
         addNode("sleep", NodeCase.SLEEP, n.build());
     }
 
+    @Override
     public void sleepUntil(WfRunVariable timestamp) {
         checkIfIsActive();
         SleepNode.Builder n = SleepNode.newBuilder().setTimestamp(assignVariable(timestamp));
         addNode("sleep", NodeCase.SLEEP, n.build());
     }
 
+    @Override
     public SpawnedThreadImpl spawnThread(ThreadFunc threadFunc, String threadName, Map<String, Object> inputVars) {
         checkIfIsActive();
         if (inputVars == null) {
@@ -625,6 +707,7 @@ public void addFailureHandlerOnWaitForThreadsNode(WaitForThreadsNodeOutputImpl n
         spec.putNodes(node.nodeName, n.build());
     }
 
+    @Override
     public void mutate(WfRunVariable lhsVar, VariableMutationType type, Object rhs) {
         checkIfIsActive();
         WfRunVariableImpl lhs = (WfRunVariableImpl) lhsVar;
@@ -635,6 +718,8 @@ public void mutate(WfRunVariable lhsVar, VariableMutationType type, Object rhs)
             mutation.setLhsJsonPath(lhs.jsonPath);
         }
 
+        mutation.setSourceVariable(assignVariable(rhs));
+
         if (NodeOutputImpl.class.isAssignableFrom(rhs.getClass())) {
             NodeOutputImpl no = (NodeOutputImpl) rhs;
             if (!no.nodeName.equals(this.lastNodeName)) {
@@ -659,6 +744,12 @@ public void mutate(WfRunVariable lhsVar, VariableMutationType type, Object rhs)
             varBuilder.setVariableName(var.name);
 
             mutation.setSourceVariable(varBuilder);
+        } else if (LHExpression.class.isAssignableFrom(rhs.getClass())) {
+            // TODO: Long term, we should deprecate all forms of mutation other than
+            // just using the `VariableAssignemnt source_variable` field.
+            //
+            // That would mean we just use `assignVariable()` for all cases.
+            mutation.setSourceVariable(assignVariable(rhs));
         } else {
             // At this point, we're going to treat it as a regular POJO, which means
             // likely a json obj.
diff --git a/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/FixedSpawnedThreadsTest.java b/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/FixedSpawnedThreadsTest.java
index 2e3ec2461..f5a753b38 100644
--- a/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/FixedSpawnedThreadsTest.java
+++ b/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/FixedSpawnedThreadsTest.java
@@ -17,8 +17,8 @@ public class FixedSpawnedThreadsTest {
 
     @BeforeEach
     void setup() {
-        when(spawnedThread1.getThreadNumberVariable()).thenReturn(new WfRunVariableImpl("thread-1", 1));
-        when(spawnedThread2.getThreadNumberVariable()).thenReturn(new WfRunVariableImpl("thread-2", 2));
+        when(spawnedThread1.getThreadNumberVariable()).thenReturn(new WfRunVariableImpl("thread-1", 1, null));
+        when(spawnedThread2.getThreadNumberVariable()).thenReturn(new WfRunVariableImpl("thread-2", 2, null));
     }
 
     @Test
@@ -29,7 +29,9 @@ void shouldBuildNodeForTwoThreadsToWaitFor() {
 
     @Test
     void shouldThrowIllegalArgumentExceptionIfThereIsANonIntegerVar() {
-        doReturn(new WfRunVariableImpl("thread-2", "2")).when(spawnedThread2).getThreadNumberVariable();
+        doReturn(new WfRunVariableImpl("thread-2", "2", null))
+                .when(spawnedThread2)
+                .getThreadNumberVariable();
         Throwable exception = catchThrowable(fixedSpawnedThreads::buildNode);
         assertThat(exception).isInstanceOfAny(IllegalArgumentException.class);
     }
diff --git a/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImplTest.java b/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImplTest.java
index 9f467c822..a41b2f99a 100644
--- a/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImplTest.java
+++ b/sdk-java/src/test/java/io/littlehorse/sdk/wfsdk/internal/WfRunVariableImplTest.java
@@ -10,7 +10,7 @@
 public class WfRunVariableImplTest {
     @Test
     void validateVariableAllowJsonPah() {
-        WfRunVariableImpl variable = new WfRunVariableImpl("my-var", VariableType.STR);
+        WfRunVariableImpl variable = new WfRunVariableImpl("my-var", VariableType.STR, null);
 
         LHMisconfigurationException e =
                 assertThrows(LHMisconfigurationException.class, () -> variable.jsonPath("&.myPath"));
diff --git a/sdk-js/src/proto/common_wfspec.ts b/sdk-js/src/proto/common_wfspec.ts
index 0487a7f2b..85696dc53 100644
--- a/sdk-js/src/proto/common_wfspec.ts
+++ b/sdk-js/src/proto/common_wfspec.ts
@@ -217,7 +217,11 @@ export interface VariableAssignment {
     | VariableAssignment_FormatString
     | undefined;
   /** Assign the value of a NodeOutput. */
-  nodeOutput?: VariableAssignment_NodeOutputReference | undefined;
+  nodeOutput?:
+    | VariableAssignment_NodeOutputReference
+    | undefined;
+  /** Assign the value of an Expression. */
+  expression?: VariableAssignment_Expression | undefined;
 }
 
 /** A FormatString formats a template String with values from the WfRun. */
@@ -244,6 +248,18 @@ export interface VariableAssignment_NodeOutputReference {
   nodeName: string;
 }
 
+/** An Expression allows you to combine multiple values into one. */
+export interface VariableAssignment_Expression {
+  /** The left-hand-side of the expression. */
+  lhs:
+    | VariableAssignment
+    | undefined;
+  /** The operator in the expression. */
+  operation: VariableMutationType;
+  /** The right-hand-side of the expression. */
+  rhs: VariableAssignment | undefined;
+}
+
 /**
  * A VariableMutation defines a modification made to one of a ThreadRun's variables.
  * The LHS determines the variable that is modified; the operation determines how
@@ -473,6 +489,7 @@ function createBaseVariableAssignment(): VariableAssignment {
     literalValue: undefined,
     formatString: undefined,
     nodeOutput: undefined,
+    expression: undefined,
   };
 }
 
@@ -493,6 +510,9 @@ export const VariableAssignment = {
     if (message.nodeOutput !== undefined) {
       VariableAssignment_NodeOutputReference.encode(message.nodeOutput, writer.uint32(42).fork()).ldelim();
     }
+    if (message.expression !== undefined) {
+      VariableAssignment_Expression.encode(message.expression, writer.uint32(50).fork()).ldelim();
+    }
     return writer;
   },
 
@@ -538,6 +558,13 @@ export const VariableAssignment = {
 
           message.nodeOutput = VariableAssignment_NodeOutputReference.decode(reader, reader.uint32());
           continue;
+        case 6:
+          if (tag !== 50) {
+            break;
+          }
+
+          message.expression = VariableAssignment_Expression.decode(reader, reader.uint32());
+          continue;
       }
       if ((tag & 7) === 4 || tag === 0) {
         break;
@@ -563,6 +590,9 @@ export const VariableAssignment = {
     message.nodeOutput = (object.nodeOutput !== undefined && object.nodeOutput !== null)
       ? VariableAssignment_NodeOutputReference.fromPartial(object.nodeOutput)
       : undefined;
+    message.expression = (object.expression !== undefined && object.expression !== null)
+      ? VariableAssignment_Expression.fromPartial(object.expression)
+      : undefined;
     return message;
   },
 };
@@ -670,6 +700,77 @@ export const VariableAssignment_NodeOutputReference = {
   },
 };
 
+function createBaseVariableAssignment_Expression(): VariableAssignment_Expression {
+  return { lhs: undefined, operation: VariableMutationType.ASSIGN, rhs: undefined };
+}
+
+export const VariableAssignment_Expression = {
+  encode(message: VariableAssignment_Expression, writer: _m0.Writer = _m0.Writer.create()): _m0.Writer {
+    if (message.lhs !== undefined) {
+      VariableAssignment.encode(message.lhs, writer.uint32(10).fork()).ldelim();
+    }
+    if (message.operation !== VariableMutationType.ASSIGN) {
+      writer.uint32(16).int32(variableMutationTypeToNumber(message.operation));
+    }
+    if (message.rhs !== undefined) {
+      VariableAssignment.encode(message.rhs, writer.uint32(26).fork()).ldelim();
+    }
+    return writer;
+  },
+
+  decode(input: _m0.Reader | Uint8Array, length?: number): VariableAssignment_Expression {
+    const reader = input instanceof _m0.Reader ? input : _m0.Reader.create(input);
+    let end = length === undefined ? reader.len : reader.pos + length;
+    const message = createBaseVariableAssignment_Expression();
+    while (reader.pos < end) {
+      const tag = reader.uint32();
+      switch (tag >>> 3) {
+        case 1:
+          if (tag !== 10) {
+            break;
+          }
+
+          message.lhs = VariableAssignment.decode(reader, reader.uint32());
+          continue;
+        case 2:
+          if (tag !== 16) {
+            break;
+          }
+
+          message.operation = variableMutationTypeFromJSON(reader.int32());
+          continue;
+        case 3:
+          if (tag !== 26) {
+            break;
+          }
+
+          message.rhs = VariableAssignment.decode(reader, reader.uint32());
+          continue;
+      }
+      if ((tag & 7) === 4 || tag === 0) {
+        break;
+      }
+      reader.skipType(tag & 7);
+    }
+    return message;
+  },
+
+  create(base?: DeepPartial<VariableAssignment_Expression>): VariableAssignment_Expression {
+    return VariableAssignment_Expression.fromPartial(base ?? {});
+  },
+  fromPartial(object: DeepPartial<VariableAssignment_Expression>): VariableAssignment_Expression {
+    const message = createBaseVariableAssignment_Expression();
+    message.lhs = (object.lhs !== undefined && object.lhs !== null)
+      ? VariableAssignment.fromPartial(object.lhs)
+      : undefined;
+    message.operation = object.operation ?? VariableMutationType.ASSIGN;
+    message.rhs = (object.rhs !== undefined && object.rhs !== null)
+      ? VariableAssignment.fromPartial(object.rhs)
+      : undefined;
+    return message;
+  },
+};
+
 function createBaseVariableMutation(): VariableMutation {
   return {
     lhsName: "",
diff --git a/sdk-js/src/proto/service.ts b/sdk-js/src/proto/service.ts
index 7127eeedd..23cdba469 100644
--- a/sdk-js/src/proto/service.ts
+++ b/sdk-js/src/proto/service.ts
@@ -8447,6 +8447,14 @@ export const LittleHorseDefinition = {
       responseStream: false,
       options: {},
     },
+    getPrincipal: {
+      name: "GetPrincipal",
+      requestType: PrincipalId,
+      requestStream: false,
+      responseType: Principal,
+      responseStream: false,
+      options: {},
+    },
     /** Returns the Principal of the caller. */
     whoami: {
       name: "Whoami",
@@ -8828,6 +8836,7 @@ export interface LittleHorseServiceImplementation<CallContextExt = {}> {
   getTenant(request: TenantId, context: CallContext & CallContextExt): Promise<DeepPartial<Tenant>>;
   /** EXPERIMENTAL: Creates an Principal. */
   putPrincipal(request: PutPrincipalRequest, context: CallContext & CallContextExt): Promise<DeepPartial<Principal>>;
+  getPrincipal(request: PrincipalId, context: CallContext & CallContextExt): Promise<DeepPartial<Principal>>;
   /** Returns the Principal of the caller. */
   whoami(request: Empty, context: CallContext & CallContextExt): Promise<DeepPartial<Principal>>;
   /** Gets the version of the LH Server. */
@@ -9203,6 +9212,7 @@ export interface LittleHorseClient<CallOptionsExt = {}> {
   getTenant(request: DeepPartial<TenantId>, options?: CallOptions & CallOptionsExt): Promise<Tenant>;
   /** EXPERIMENTAL: Creates an Principal. */
   putPrincipal(request: DeepPartial<PutPrincipalRequest>, options?: CallOptions & CallOptionsExt): Promise<Principal>;
+  getPrincipal(request: DeepPartial<PrincipalId>, options?: CallOptions & CallOptionsExt): Promise<Principal>;
   /** Returns the Principal of the caller. */
   whoami(request: DeepPartial<Empty>, options?: CallOptions & CallOptionsExt): Promise<Principal>;
   /** Gets the version of the LH Server. */
diff --git a/sdk-python/littlehorse/model/__init__.py b/sdk-python/littlehorse/model/__init__.py
index c956189c7..85f573b7e 100644
--- a/sdk-python/littlehorse/model/__init__.py
+++ b/sdk-python/littlehorse/model/__init__.py
@@ -5,8 +5,8 @@
 from .node_run_pb2 import *
 from .object_id_pb2 import *
 from .scheduled_wf_run_pb2 import *
-from .service_pb2_grpc import *
 from .service_pb2 import *
+from .service_pb2_grpc import *
 from .task_def_pb2 import *
 from .task_run_pb2 import *
 from .user_tasks_pb2 import *
diff --git a/sdk-python/littlehorse/model/common_wfspec_pb2.py b/sdk-python/littlehorse/model/common_wfspec_pb2.py
index 879cef26f..e209ba371 100644
--- a/sdk-python/littlehorse/model/common_wfspec_pb2.py
+++ b/sdk-python/littlehorse/model/common_wfspec_pb2.py
@@ -16,7 +16,7 @@
 import littlehorse.model.object_id_pb2 as object__id__pb2
 
 
-DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(b'\n\x13\x63ommon_wfspec.proto\x12\x0blittlehorse\x1a\x12\x63ommon_enums.proto\x1a\x0evariable.proto\x1a\x0fobject_id.proto\"\xbf\x03\n\x12VariableAssignment\x12\x16\n\tjson_path\x18\x01 \x01(\tH\x01\x88\x01\x01\x12\x17\n\rvariable_name\x18\x02 \x01(\tH\x00\x12\x33\n\rliteral_value\x18\x03 \x01(\x0b\x32\x1a.littlehorse.VariableValueH\x00\x12\x45\n\rformat_string\x18\x04 \x01(\x0b\x32,.littlehorse.VariableAssignment.FormatStringH\x00\x12J\n\x0bnode_output\x18\x05 \x01(\x0b\x32\x33.littlehorse.VariableAssignment.NodeOutputReferenceH\x00\x1an\n\x0c\x46ormatString\x12/\n\x06\x66ormat\x18\x01 \x01(\x0b\x32\x1f.littlehorse.VariableAssignment\x12-\n\x04\x61rgs\x18\x02 \x03(\x0b\x32\x1f.littlehorse.VariableAssignment\x1a(\n\x13NodeOutputReference\x12\x11\n\tnode_name\x18\x01 \x01(\tB\x08\n\x06sourceB\x0c\n\n_json_path\"\x85\x03\n\x10VariableMutation\x12\x10\n\x08lhs_name\x18\x01 \x01(\t\x12\x1a\n\rlhs_json_path\x18\x02 \x01(\tH\x01\x88\x01\x01\x12\x34\n\toperation\x18\x03 \x01(\x0e\x32!.littlehorse.VariableMutationType\x12:\n\x0fsource_variable\x18\x04 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x00\x12\x33\n\rliteral_value\x18\x05 \x01(\x0b\x32\x1a.littlehorse.VariableValueH\x00\x12\x45\n\x0bnode_output\x18\x06 \x01(\x0b\x32..littlehorse.VariableMutation.NodeOutputSourceH\x00\x1a\x36\n\x10NodeOutputSource\x12\x15\n\x08jsonpath\x18\n \x01(\tH\x00\x88\x01\x01\x42\x0b\n\t_jsonpathB\x0b\n\trhs_valueB\x10\n\x0e_lhs_json_path\"\xa4\x01\n\x0bVariableDef\x12\'\n\x04type\x18\x01 \x01(\x0e\x32\x19.littlehorse.VariableType\x12\x0c\n\x04name\x18\x02 \x01(\t\x12\x36\n\rdefault_value\x18\x03 \x01(\x0b\x32\x1a.littlehorse.VariableValueH\x00\x88\x01\x01\x12\x14\n\x0cmasked_value\x18\x04 \x01(\x08\x42\x10\n\x0e_default_value\"\xef\x04\n\x0fUTActionTrigger\x12\x34\n\x04task\x18\x01 \x01(\x0b\x32$.littlehorse.UTActionTrigger.UTATaskH\x00\x12\x38\n\x06\x63\x61ncel\x18\x02 \x01(\x0b\x32&.littlehorse.UTActionTrigger.UTACancelH\x00\x12<\n\x08reassign\x18\x03 \x01(\x0b\x32(.littlehorse.UTActionTrigger.UTAReassignH\x00\x12\x36\n\rdelay_seconds\x18\x05 \x01(\x0b\x32\x1f.littlehorse.VariableAssignment\x12\x31\n\x04hook\x18\x06 \x01(\x0e\x32#.littlehorse.UTActionTrigger.UTHook\x1a\x0b\n\tUTACancel\x1a`\n\x07UTATask\x12#\n\x04task\x18\x01 \x01(\x0b\x32\x15.littlehorse.TaskNode\x12\x30\n\tmutations\x18\x02 \x03(\x0b\x32\x1d.littlehorse.VariableMutation\x1a\x99\x01\n\x0bUTAReassign\x12\x35\n\x07user_id\x18\x01 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x00\x88\x01\x01\x12\x38\n\nuser_group\x18\x02 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x01\x88\x01\x01\x42\n\n\x08_user_idB\r\n\x0b_user_group\".\n\x06UTHook\x12\x0e\n\nON_ARRIVAL\x10\x00\x12\x14\n\x10ON_TASK_ASSIGNED\x10\x01\x42\x08\n\x06\x61\x63tion\"c\n\x1d\x45xponentialBackoffRetryPolicy\x12\x18\n\x10\x62\x61se_interval_ms\x18\x01 \x01(\x05\x12\x14\n\x0cmax_delay_ms\x18\x02 \x01(\x03\x12\x12\n\nmultiplier\x18\x03 \x01(\x02\"\xc9\x02\n\x08TaskNode\x12-\n\x0btask_def_id\x18\x01 \x01(\x0b\x32\x16.littlehorse.TaskDefIdH\x00\x12\x37\n\x0c\x64ynamic_task\x18\x06 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x00\x12\x17\n\x0ftimeout_seconds\x18\x02 \x01(\x05\x12\x0f\n\x07retries\x18\x03 \x01(\x05\x12L\n\x13\x65xponential_backoff\x18\x05 \x01(\x0b\x32*.littlehorse.ExponentialBackoffRetryPolicyH\x01\x88\x01\x01\x12\x32\n\tvariables\x18\x04 \x03(\x0b\x32\x1f.littlehorse.VariableAssignmentB\x11\n\x0ftask_to_executeB\x16\n\x14_exponential_backoff*\x98\x01\n\x14VariableMutationType\x12\n\n\x06\x41SSIGN\x10\x00\x12\x07\n\x03\x41\x44\x44\x10\x01\x12\n\n\x06\x45XTEND\x10\x02\x12\x0c\n\x08SUBTRACT\x10\x03\x12\x0c\n\x08MULTIPLY\x10\x04\x12\n\n\x06\x44IVIDE\x10\x05\x12\x15\n\x11REMOVE_IF_PRESENT\x10\x06\x12\x10\n\x0cREMOVE_INDEX\x10\x07\x12\x0e\n\nREMOVE_KEY\x10\x08*\x84\x01\n\nComparator\x12\r\n\tLESS_THAN\x10\x00\x12\x10\n\x0cGREATER_THAN\x10\x01\x12\x10\n\x0cLESS_THAN_EQ\x10\x02\x12\x13\n\x0fGREATER_THAN_EQ\x10\x03\x12\n\n\x06\x45QUALS\x10\x04\x12\x0e\n\nNOT_EQUALS\x10\x05\x12\x06\n\x02IN\x10\x06\x12\n\n\x06NOT_IN\x10\x07\x42I\n\x1fio.littlehorse.sdk.common.protoP\x01Z\t.;lhproto\xaa\x02\x18LittleHorse.Common.Protob\x06proto3')
+DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(b'\n\x13\x63ommon_wfspec.proto\x12\x0blittlehorse\x1a\x12\x63ommon_enums.proto\x1a\x0evariable.proto\x1a\x0fobject_id.proto\"\xa2\x05\n\x12VariableAssignment\x12\x16\n\tjson_path\x18\x01 \x01(\tH\x01\x88\x01\x01\x12\x17\n\rvariable_name\x18\x02 \x01(\tH\x00\x12\x33\n\rliteral_value\x18\x03 \x01(\x0b\x32\x1a.littlehorse.VariableValueH\x00\x12\x45\n\rformat_string\x18\x04 \x01(\x0b\x32,.littlehorse.VariableAssignment.FormatStringH\x00\x12J\n\x0bnode_output\x18\x05 \x01(\x0b\x32\x33.littlehorse.VariableAssignment.NodeOutputReferenceH\x00\x12@\n\nexpression\x18\x06 \x01(\x0b\x32*.littlehorse.VariableAssignment.ExpressionH\x00\x1an\n\x0c\x46ormatString\x12/\n\x06\x66ormat\x18\x01 \x01(\x0b\x32\x1f.littlehorse.VariableAssignment\x12-\n\x04\x61rgs\x18\x02 \x03(\x0b\x32\x1f.littlehorse.VariableAssignment\x1a(\n\x13NodeOutputReference\x12\x11\n\tnode_name\x18\x01 \x01(\t\x1a\x9e\x01\n\nExpression\x12,\n\x03lhs\x18\x01 \x01(\x0b\x32\x1f.littlehorse.VariableAssignment\x12\x34\n\toperation\x18\x02 \x01(\x0e\x32!.littlehorse.VariableMutationType\x12,\n\x03rhs\x18\x03 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentB\x08\n\x06sourceB\x0c\n\n_json_path\"\x85\x03\n\x10VariableMutation\x12\x10\n\x08lhs_name\x18\x01 \x01(\t\x12\x1a\n\rlhs_json_path\x18\x02 \x01(\tH\x01\x88\x01\x01\x12\x34\n\toperation\x18\x03 \x01(\x0e\x32!.littlehorse.VariableMutationType\x12:\n\x0fsource_variable\x18\x04 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x00\x12\x33\n\rliteral_value\x18\x05 \x01(\x0b\x32\x1a.littlehorse.VariableValueH\x00\x12\x45\n\x0bnode_output\x18\x06 \x01(\x0b\x32..littlehorse.VariableMutation.NodeOutputSourceH\x00\x1a\x36\n\x10NodeOutputSource\x12\x15\n\x08jsonpath\x18\n \x01(\tH\x00\x88\x01\x01\x42\x0b\n\t_jsonpathB\x0b\n\trhs_valueB\x10\n\x0e_lhs_json_path\"\xa4\x01\n\x0bVariableDef\x12\'\n\x04type\x18\x01 \x01(\x0e\x32\x19.littlehorse.VariableType\x12\x0c\n\x04name\x18\x02 \x01(\t\x12\x36\n\rdefault_value\x18\x03 \x01(\x0b\x32\x1a.littlehorse.VariableValueH\x00\x88\x01\x01\x12\x14\n\x0cmasked_value\x18\x04 \x01(\x08\x42\x10\n\x0e_default_value\"\xef\x04\n\x0fUTActionTrigger\x12\x34\n\x04task\x18\x01 \x01(\x0b\x32$.littlehorse.UTActionTrigger.UTATaskH\x00\x12\x38\n\x06\x63\x61ncel\x18\x02 \x01(\x0b\x32&.littlehorse.UTActionTrigger.UTACancelH\x00\x12<\n\x08reassign\x18\x03 \x01(\x0b\x32(.littlehorse.UTActionTrigger.UTAReassignH\x00\x12\x36\n\rdelay_seconds\x18\x05 \x01(\x0b\x32\x1f.littlehorse.VariableAssignment\x12\x31\n\x04hook\x18\x06 \x01(\x0e\x32#.littlehorse.UTActionTrigger.UTHook\x1a\x0b\n\tUTACancel\x1a`\n\x07UTATask\x12#\n\x04task\x18\x01 \x01(\x0b\x32\x15.littlehorse.TaskNode\x12\x30\n\tmutations\x18\x02 \x03(\x0b\x32\x1d.littlehorse.VariableMutation\x1a\x99\x01\n\x0bUTAReassign\x12\x35\n\x07user_id\x18\x01 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x00\x88\x01\x01\x12\x38\n\nuser_group\x18\x02 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x01\x88\x01\x01\x42\n\n\x08_user_idB\r\n\x0b_user_group\".\n\x06UTHook\x12\x0e\n\nON_ARRIVAL\x10\x00\x12\x14\n\x10ON_TASK_ASSIGNED\x10\x01\x42\x08\n\x06\x61\x63tion\"c\n\x1d\x45xponentialBackoffRetryPolicy\x12\x18\n\x10\x62\x61se_interval_ms\x18\x01 \x01(\x05\x12\x14\n\x0cmax_delay_ms\x18\x02 \x01(\x03\x12\x12\n\nmultiplier\x18\x03 \x01(\x02\"\xc9\x02\n\x08TaskNode\x12-\n\x0btask_def_id\x18\x01 \x01(\x0b\x32\x16.littlehorse.TaskDefIdH\x00\x12\x37\n\x0c\x64ynamic_task\x18\x06 \x01(\x0b\x32\x1f.littlehorse.VariableAssignmentH\x00\x12\x17\n\x0ftimeout_seconds\x18\x02 \x01(\x05\x12\x0f\n\x07retries\x18\x03 \x01(\x05\x12L\n\x13\x65xponential_backoff\x18\x05 \x01(\x0b\x32*.littlehorse.ExponentialBackoffRetryPolicyH\x01\x88\x01\x01\x12\x32\n\tvariables\x18\x04 \x03(\x0b\x32\x1f.littlehorse.VariableAssignmentB\x11\n\x0ftask_to_executeB\x16\n\x14_exponential_backoff*\x98\x01\n\x14VariableMutationType\x12\n\n\x06\x41SSIGN\x10\x00\x12\x07\n\x03\x41\x44\x44\x10\x01\x12\n\n\x06\x45XTEND\x10\x02\x12\x0c\n\x08SUBTRACT\x10\x03\x12\x0c\n\x08MULTIPLY\x10\x04\x12\n\n\x06\x44IVIDE\x10\x05\x12\x15\n\x11REMOVE_IF_PRESENT\x10\x06\x12\x10\n\x0cREMOVE_INDEX\x10\x07\x12\x0e\n\nREMOVE_KEY\x10\x08*\x84\x01\n\nComparator\x12\r\n\tLESS_THAN\x10\x00\x12\x10\n\x0cGREATER_THAN\x10\x01\x12\x10\n\x0cLESS_THAN_EQ\x10\x02\x12\x13\n\x0fGREATER_THAN_EQ\x10\x03\x12\n\n\x06\x45QUALS\x10\x04\x12\x0e\n\nNOT_EQUALS\x10\x05\x12\x06\n\x02IN\x10\x06\x12\n\n\x06NOT_IN\x10\x07\x42I\n\x1fio.littlehorse.sdk.common.protoP\x01Z\t.;lhproto\xaa\x02\x18LittleHorse.Common.Protob\x06proto3')
 
 _globals = globals()
 _builder.BuildMessageAndEnumDescriptors(DESCRIPTOR, _globals)
@@ -25,34 +25,36 @@
 
   DESCRIPTOR._options = None
   DESCRIPTOR._serialized_options = b'\n\037io.littlehorse.sdk.common.protoP\001Z\t.;lhproto\252\002\030LittleHorse.Common.Proto'
-  _globals['_VARIABLEMUTATIONTYPE']._serialized_start=2158
-  _globals['_VARIABLEMUTATIONTYPE']._serialized_end=2310
-  _globals['_COMPARATOR']._serialized_start=2313
-  _globals['_COMPARATOR']._serialized_end=2445
+  _globals['_VARIABLEMUTATIONTYPE']._serialized_start=2385
+  _globals['_VARIABLEMUTATIONTYPE']._serialized_end=2537
+  _globals['_COMPARATOR']._serialized_start=2540
+  _globals['_COMPARATOR']._serialized_end=2672
   _globals['_VARIABLEASSIGNMENT']._serialized_start=90
-  _globals['_VARIABLEASSIGNMENT']._serialized_end=537
-  _globals['_VARIABLEASSIGNMENT_FORMATSTRING']._serialized_start=361
-  _globals['_VARIABLEASSIGNMENT_FORMATSTRING']._serialized_end=471
-  _globals['_VARIABLEASSIGNMENT_NODEOUTPUTREFERENCE']._serialized_start=473
-  _globals['_VARIABLEASSIGNMENT_NODEOUTPUTREFERENCE']._serialized_end=513
-  _globals['_VARIABLEMUTATION']._serialized_start=540
-  _globals['_VARIABLEMUTATION']._serialized_end=929
-  _globals['_VARIABLEMUTATION_NODEOUTPUTSOURCE']._serialized_start=844
-  _globals['_VARIABLEMUTATION_NODEOUTPUTSOURCE']._serialized_end=898
-  _globals['_VARIABLEDEF']._serialized_start=932
-  _globals['_VARIABLEDEF']._serialized_end=1096
-  _globals['_UTACTIONTRIGGER']._serialized_start=1099
-  _globals['_UTACTIONTRIGGER']._serialized_end=1722
-  _globals['_UTACTIONTRIGGER_UTACANCEL']._serialized_start=1399
-  _globals['_UTACTIONTRIGGER_UTACANCEL']._serialized_end=1410
-  _globals['_UTACTIONTRIGGER_UTATASK']._serialized_start=1412
-  _globals['_UTACTIONTRIGGER_UTATASK']._serialized_end=1508
-  _globals['_UTACTIONTRIGGER_UTAREASSIGN']._serialized_start=1511
-  _globals['_UTACTIONTRIGGER_UTAREASSIGN']._serialized_end=1664
-  _globals['_UTACTIONTRIGGER_UTHOOK']._serialized_start=1666
-  _globals['_UTACTIONTRIGGER_UTHOOK']._serialized_end=1712
-  _globals['_EXPONENTIALBACKOFFRETRYPOLICY']._serialized_start=1724
-  _globals['_EXPONENTIALBACKOFFRETRYPOLICY']._serialized_end=1823
-  _globals['_TASKNODE']._serialized_start=1826
-  _globals['_TASKNODE']._serialized_end=2155
+  _globals['_VARIABLEASSIGNMENT']._serialized_end=764
+  _globals['_VARIABLEASSIGNMENT_FORMATSTRING']._serialized_start=427
+  _globals['_VARIABLEASSIGNMENT_FORMATSTRING']._serialized_end=537
+  _globals['_VARIABLEASSIGNMENT_NODEOUTPUTREFERENCE']._serialized_start=539
+  _globals['_VARIABLEASSIGNMENT_NODEOUTPUTREFERENCE']._serialized_end=579
+  _globals['_VARIABLEASSIGNMENT_EXPRESSION']._serialized_start=582
+  _globals['_VARIABLEASSIGNMENT_EXPRESSION']._serialized_end=740
+  _globals['_VARIABLEMUTATION']._serialized_start=767
+  _globals['_VARIABLEMUTATION']._serialized_end=1156
+  _globals['_VARIABLEMUTATION_NODEOUTPUTSOURCE']._serialized_start=1071
+  _globals['_VARIABLEMUTATION_NODEOUTPUTSOURCE']._serialized_end=1125
+  _globals['_VARIABLEDEF']._serialized_start=1159
+  _globals['_VARIABLEDEF']._serialized_end=1323
+  _globals['_UTACTIONTRIGGER']._serialized_start=1326
+  _globals['_UTACTIONTRIGGER']._serialized_end=1949
+  _globals['_UTACTIONTRIGGER_UTACANCEL']._serialized_start=1626
+  _globals['_UTACTIONTRIGGER_UTACANCEL']._serialized_end=1637
+  _globals['_UTACTIONTRIGGER_UTATASK']._serialized_start=1639
+  _globals['_UTACTIONTRIGGER_UTATASK']._serialized_end=1735
+  _globals['_UTACTIONTRIGGER_UTAREASSIGN']._serialized_start=1738
+  _globals['_UTACTIONTRIGGER_UTAREASSIGN']._serialized_end=1891
+  _globals['_UTACTIONTRIGGER_UTHOOK']._serialized_start=1893
+  _globals['_UTACTIONTRIGGER_UTHOOK']._serialized_end=1939
+  _globals['_EXPONENTIALBACKOFFRETRYPOLICY']._serialized_start=1951
+  _globals['_EXPONENTIALBACKOFFRETRYPOLICY']._serialized_end=2050
+  _globals['_TASKNODE']._serialized_start=2053
+  _globals['_TASKNODE']._serialized_end=2382
 # @@protoc_insertion_point(module_scope)
diff --git a/sdk-python/littlehorse/model/common_wfspec_pb2.pyi b/sdk-python/littlehorse/model/common_wfspec_pb2.pyi
index f1054dd0f..1e3ebffa6 100644
--- a/sdk-python/littlehorse/model/common_wfspec_pb2.pyi
+++ b/sdk-python/littlehorse/model/common_wfspec_pb2.pyi
@@ -50,7 +50,7 @@ IN: Comparator
 NOT_IN: Comparator
 
 class VariableAssignment(_message.Message):
-    __slots__ = ["json_path", "variable_name", "literal_value", "format_string", "node_output"]
+    __slots__ = ["json_path", "variable_name", "literal_value", "format_string", "node_output", "expression"]
     class FormatString(_message.Message):
         __slots__ = ["format", "args"]
         FORMAT_FIELD_NUMBER: _ClassVar[int]
@@ -63,17 +63,28 @@ class VariableAssignment(_message.Message):
         NODE_NAME_FIELD_NUMBER: _ClassVar[int]
         node_name: str
         def __init__(self, node_name: _Optional[str] = ...) -> None: ...
+    class Expression(_message.Message):
+        __slots__ = ["lhs", "operation", "rhs"]
+        LHS_FIELD_NUMBER: _ClassVar[int]
+        OPERATION_FIELD_NUMBER: _ClassVar[int]
+        RHS_FIELD_NUMBER: _ClassVar[int]
+        lhs: VariableAssignment
+        operation: VariableMutationType
+        rhs: VariableAssignment
+        def __init__(self, lhs: _Optional[_Union[VariableAssignment, _Mapping]] = ..., operation: _Optional[_Union[VariableMutationType, str]] = ..., rhs: _Optional[_Union[VariableAssignment, _Mapping]] = ...) -> None: ...
     JSON_PATH_FIELD_NUMBER: _ClassVar[int]
     VARIABLE_NAME_FIELD_NUMBER: _ClassVar[int]
     LITERAL_VALUE_FIELD_NUMBER: _ClassVar[int]
     FORMAT_STRING_FIELD_NUMBER: _ClassVar[int]
     NODE_OUTPUT_FIELD_NUMBER: _ClassVar[int]
+    EXPRESSION_FIELD_NUMBER: _ClassVar[int]
     json_path: str
     variable_name: str
     literal_value: _variable_pb2.VariableValue
     format_string: VariableAssignment.FormatString
     node_output: VariableAssignment.NodeOutputReference
-    def __init__(self, json_path: _Optional[str] = ..., variable_name: _Optional[str] = ..., literal_value: _Optional[_Union[_variable_pb2.VariableValue, _Mapping]] = ..., format_string: _Optional[_Union[VariableAssignment.FormatString, _Mapping]] = ..., node_output: _Optional[_Union[VariableAssignment.NodeOutputReference, _Mapping]] = ...) -> None: ...
+    expression: VariableAssignment.Expression
+    def __init__(self, json_path: _Optional[str] = ..., variable_name: _Optional[str] = ..., literal_value: _Optional[_Union[_variable_pb2.VariableValue, _Mapping]] = ..., format_string: _Optional[_Union[VariableAssignment.FormatString, _Mapping]] = ..., node_output: _Optional[_Union[VariableAssignment.NodeOutputReference, _Mapping]] = ..., expression: _Optional[_Union[VariableAssignment.Expression, _Mapping]] = ...) -> None: ...
 
 class VariableMutation(_message.Message):
     __slots__ = ["lhs_name", "lhs_json_path", "operation", "source_variable", "literal_value", "node_output"]
diff --git a/sdk-python/littlehorse/model/service_pb2.py b/sdk-python/littlehorse/model/service_pb2.py
index dc8a8eb6a..f5c4b5dfe 100644
--- a/sdk-python/littlehorse/model/service_pb2.py
+++ b/sdk-python/littlehorse/model/service_pb2.py
@@ -29,7 +29,7 @@
 import littlehorse.model.scheduled_wf_run_pb2 as scheduled__wf__run__pb2
 
 
-DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(b'\n\rservice.proto\x12\x0blittlehorse\x1a\x1fgoogle/protobuf/timestamp.proto\x1a\x1bgoogle/protobuf/empty.proto\x1a\x13\x63ommon_wfspec.proto\x1a\x12\x63ommon_enums.proto\x1a\x0fobject_id.proto\x1a\x0evariable.proto\x1a\x14\x65xternal_event.proto\x1a\x0cwf_run.proto\x1a\x0enode_run.proto\x1a\x0etask_run.proto\x1a\x10user_tasks.proto\x1a\rwf_spec.proto\x1a\x0etask_def.proto\x1a\nacls.proto\x1a\x14workflow_event.proto\x1a\x16scheduled_wf_run.proto\"+\n\x1bGetLatestUserTaskDefRequest\x12\x0c\n\x04name\x18\x01 \x01(\t\"\xd3\x03\n\x10PutWfSpecRequest\x12\x0c\n\x04name\x18\x01 \x01(\t\x12\x44\n\x0cthread_specs\x18\x05 \x03(\x0b\x32..littlehorse.PutWfSpecRequest.ThreadSpecsEntry\x12\x1e\n\x16\x65ntrypoint_thread_name\x18\x06 \x01(\t\x12\x43\n\x10retention_policy\x18\x08 \x01(\x0b\x32$.littlehorse.WorkflowRetentionPolicyH\x00\x88\x01\x01\x12\x46\n\x0eparent_wf_spec\x18\t 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\x01(\tH\x00\x88\x01\x01\x42\x19\n\x17_pre_release_identifier*P\n\x11\x41llowedUpdateType\x12\x0f\n\x0b\x41LL_UPDATES\x10\x00\x12\x1a\n\x16MINOR_REVISION_UPDATES\x10\x01\x12\x0e\n\nNO_UPDATES\x10\x02\x32\xae\x30\n\x0bLittleHorse\x12\x44\n\nPutTaskDef\x12\x1e.littlehorse.PutTaskDefRequest\x1a\x14.littlehorse.TaskDef\"\x00\x12<\n\nGetTaskDef\x12\x16.littlehorse.TaskDefId\x1a\x14.littlehorse.TaskDef\"\x00\x12L\n\x12GetTaskWorkerGroup\x12\x16.littlehorse.TaskDefId\x1a\x1c.littlehorse.TaskWorkerGroup\"\x00\x12_\n\x13PutExternalEventDef\x12\'.littlehorse.PutExternalEventDefRequest\x1a\x1d.littlehorse.ExternalEventDef\"\x00\x12W\n\x13GetExternalEventDef\x12\x1f.littlehorse.ExternalEventDefId\x1a\x1d.littlehorse.ExternalEventDef\"\x00\x12_\n\x13PutWorkflowEventDef\x12\'.littlehorse.PutWorkflowEventDefRequest\x1a\x1d.littlehorse.WorkflowEventDef\"\x00\x12\x41\n\tPutWfSpec\x12\x1d.littlehorse.PutWfSpecRequest\x1a\x13.littlehorse.WfSpec\"\x00\x12\x39\n\tGetWfSpec\x12\x15.littlehorse.WfSpecId\x1a\x13.littlehorse.WfSpec\"\x00\x12M\n\x0fGetLatestWfSpec\x12#.littlehorse.GetLatestWfSpecRequest\x1a\x13.littlehorse.WfSpec\"\x00\x12I\n\rMigrateWfSpec\x12!.littlehorse.MigrateWfSpecRequest\x1a\x13.littlehorse.WfSpec\"\x00\x12P\n\x0ePutUserTaskDef\x12\".littlehorse.PutUserTaskDefRequest\x1a\x18.littlehorse.UserTaskDef\"\x00\x12H\n\x0eGetUserTaskDef\x12\x1a.littlehorse.UserTaskDefId\x1a\x18.littlehorse.UserTaskDef\"\x00\x12\\\n\x14GetLatestUserTaskDef\x12(.littlehorse.GetLatestUserTaskDefRequest\x1a\x18.littlehorse.UserTaskDef\"\x00\x12\x38\n\x05RunWf\x12\x19.littlehorse.RunWfRequest\x1a\x12.littlehorse.WfRun\"\x00\x12K\n\nScheduleWf\x12\x1e.littlehorse.ScheduleWfRequest\x1a\x1b.littlehorse.ScheduledWfRun\"\x00\x12\x65\n\x14SearchScheduledWfRun\x12(.littlehorse.SearchScheduledWfRunRequest\x1a!.littlehorse.ScheduledWfRunIdList\"\x00\x12Q\n\x11GetScheduledWfRun\x12\x1d.littlehorse.ScheduledWfRunId\x1a\x1b.littlehorse.ScheduledWfRun\"\x00\x12\x36\n\x08GetWfRun\x12\x14.littlehorse.WfRunId\x1a\x12.littlehorse.WfRun\"\x00\x12H\n\x0eGetUserTaskRun\x12\x1a.littlehorse.UserTaskRunId\x1a\x18.littlehorse.UserTaskRun\"\x00\x12T\n\x11\x41ssignUserTaskRun\x12%.littlehorse.AssignUserTaskRunRequest\x1a\x16.google.protobuf.Empty\"\x00\x12X\n\x13\x43ompleteUserTaskRun\x12\'.littlehorse.CompleteUserTaskRunRequest\x1a\x16.google.protobuf.Empty\"\x00\x12T\n\x11\x43\x61ncelUserTaskRun\x12%.littlehorse.CancelUserTaskRunRequest\x1a\x16.google.protobuf.Empty\"\x00\x12\x62\n\x17SaveUserTaskRunProgress\x12+.littlehorse.SaveUserTaskRunProgressRequest\x1a\x18.littlehorse.UserTaskRun\"\x00\x12W\n\x10ListUserTaskRuns\x12#.littlehorse.ListUserTaskRunRequest\x1a\x1c.littlehorse.UserTaskRunList\"\x00\x12<\n\nGetNodeRun\x12\x16.littlehorse.NodeRunId\x1a\x14.littlehorse.NodeRun\"\x00\x12L\n\x0cListNodeRuns\x12 .littlehorse.ListNodeRunsRequest\x1a\x18.littlehorse.NodeRunList\"\x00\x12<\n\nGetTaskRun\x12\x16.littlehorse.TaskRunId\x1a\x14.littlehorse.TaskRun\"\x00\x12L\n\x0cListTaskRuns\x12 .littlehorse.ListTaskRunsRequest\x1a\x18.littlehorse.TaskRunList\"\x00\x12?\n\x0bGetVariable\x12\x17.littlehorse.VariableId\x1a\x15.littlehorse.Variable\"\x00\x12O\n\rListVariables\x12!.littlehorse.ListVariablesRequest\x1a\x19.littlehorse.VariableList\"\x00\x12V\n\x10PutExternalEvent\x12$.littlehorse.PutExternalEventRequest\x1a\x1a.littlehorse.ExternalEvent\"\x00\x12N\n\x10GetExternalEvent\x12\x1c.littlehorse.ExternalEventId\x1a\x1a.littlehorse.ExternalEvent\"\x00\x12Z\n\x12\x41waitWorkflowEvent\x12&.littlehorse.AwaitWorkflowEventRequest\x1a\x1a.littlehorse.WorkflowEvent\"\x00\x12W\n\x13GetWorkflowEventDef\x12\x1f.littlehorse.WorkflowEventDefId\x1a\x1d.littlehorse.WorkflowEventDef\"\x00\x12N\n\x10GetWorkflowEvent\x12\x1c.littlehorse.WorkflowEventId\x1a\x1a.littlehorse.WorkflowEvent\"\x00\x12^\n\x12ListExternalEvents\x12&.littlehorse.ListExternalEventsRequest\x1a\x1e.littlehorse.ExternalEventList\"\x00\x12^\n\x12ListWorkflowEvents\x12&.littlehorse.ListWorkflowEventsRequest\x1a\x1e.littlehorse.WorkflowEventList\"\x00\x12J\n\x0bSearchWfRun\x12\x1f.littlehorse.SearchWfRunRequest\x1a\x18.littlehorse.WfRunIdList\"\x00\x12P\n\rSearchNodeRun\x12!.littlehorse.SearchNodeRunRequest\x1a\x1a.littlehorse.NodeRunIdList\"\x00\x12P\n\rSearchTaskRun\x12!.littlehorse.SearchTaskRunRequest\x1a\x1a.littlehorse.TaskRunIdList\"\x00\x12\\\n\x11SearchUserTaskRun\x12%.littlehorse.SearchUserTaskRunRequest\x1a\x1e.littlehorse.UserTaskRunIdList\"\x00\x12S\n\x0eSearchVariable\x12\".littlehorse.SearchVariableRequest\x1a\x1b.littlehorse.VariableIdList\"\x00\x12\x62\n\x13SearchExternalEvent\x12\'.littlehorse.SearchExternalEventRequest\x1a 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.littlehorse.SearchTenantRequest\x1a\x19.littlehorse.TenantIdList\"\x00\x12V\n\x0fSearchPrincipal\x12#.littlehorse.SearchPrincipalRequest\x1a\x1c.littlehorse.PrincipalIdList\"\x00\x12g\n\x12RegisterTaskWorker\x12&.littlehorse.RegisterTaskWorkerRequest\x1a\'.littlehorse.RegisterTaskWorkerResponse\"\x00\x12M\n\x08PollTask\x12\x1c.littlehorse.PollTaskRequest\x1a\x1d.littlehorse.PollTaskResponse\"\x00(\x01\x30\x01\x12\x42\n\nReportTask\x12\x1a.littlehorse.ReportTaskRun\x1a\x16.google.protobuf.Empty\"\x00\x12\x44\n\tStopWfRun\x12\x1d.littlehorse.StopWfRunRequest\x1a\x16.google.protobuf.Empty\"\x00\x12H\n\x0bResumeWfRun\x12\x1f.littlehorse.ResumeWfRunRequest\x1a\x16.google.protobuf.Empty\"\x00\x12L\n\x0fRescueThreadRun\x12#.littlehorse.RescueThreadRunRequest\x1a\x12.littlehorse.WfRun\"\x00\x12H\n\x0b\x44\x65leteWfRun\x12\x1f.littlehorse.DeleteWfRunRequest\x1a\x16.google.protobuf.Empty\"\x00\x12L\n\rDeleteTaskDef\x12!.littlehorse.DeleteTaskDefRequest\x1a\x16.google.protobuf.Empty\"\x00\x12J\n\x0c\x44\x65leteWfSpec\x12 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.littlehorse.PutPrincipalRequest\x1a\x16.littlehorse.Principal\"\x00\x12\x42\n\x0cGetPrincipal\x12\x18.littlehorse.PrincipalId\x1a\x16.littlehorse.Principal\"\x00\x12:\n\x06Whoami\x12\x16.google.protobuf.Empty\x1a\x16.littlehorse.Principal\"\x00\x12H\n\x10GetServerVersion\x12\x16.google.protobuf.Empty\x1a\x1a.littlehorse.ServerVersion\"\x00\x42I\n\x1fio.littlehorse.sdk.common.protoP\x01Z\t.;lhproto\xaa\x02\x18LittleHorse.Common.Protob\x06proto3')
 
 _globals = globals()
 _builder.BuildMessageAndEnumDescriptors(DESCRIPTOR, _globals)
@@ -229,5 +229,5 @@
   _globals['_SERVERVERSION']._serialized_start=13303
   _globals['_SERVERVERSION']._serialized_end=13451
   _globals['_LITTLEHORSE']._serialized_start=13536
-  _globals['_LITTLEHORSE']._serialized_end=19658
+  _globals['_LITTLEHORSE']._serialized_end=19726
 # @@protoc_insertion_point(module_scope)
diff --git a/sdk-python/littlehorse/model/service_pb2_grpc.py b/sdk-python/littlehorse/model/service_pb2_grpc.py
index 0f88f23f3..1fcee5ee9 100644
--- a/sdk-python/littlehorse/model/service_pb2_grpc.py
+++ b/sdk-python/littlehorse/model/service_pb2_grpc.py
@@ -387,6 +387,11 @@ def __init__(self, channel):
                 request_serializer=acls__pb2.PutPrincipalRequest.SerializeToString,
                 response_deserializer=acls__pb2.Principal.FromString,
                 )
+        self.GetPrincipal = channel.unary_unary(
+                '/littlehorse.LittleHorse/GetPrincipal',
+                request_serializer=object__id__pb2.PrincipalId.SerializeToString,
+                response_deserializer=acls__pb2.Principal.FromString,
+                )
         self.Whoami = channel.unary_unary(
                 '/littlehorse.LittleHorse/Whoami',
                 request_serializer=google_dot_protobuf_dot_empty__pb2.Empty.SerializeToString,
@@ -961,6 +966,12 @@ def PutPrincipal(self, request, context):
         context.set_details('Method not implemented!')
         raise NotImplementedError('Method not implemented!')
 
+    def GetPrincipal(self, request, context):
+        """Missing associated documentation comment in .proto file."""
+        context.set_code(grpc.StatusCode.UNIMPLEMENTED)
+        context.set_details('Method not implemented!')
+        raise NotImplementedError('Method not implemented!')
+
     def Whoami(self, request, context):
         """Returns the Principal of the caller.
         """
@@ -1338,6 +1349,11 @@ def add_LittleHorseServicer_to_server(servicer, server):
                     request_deserializer=acls__pb2.PutPrincipalRequest.FromString,
                     response_serializer=acls__pb2.Principal.SerializeToString,
             ),
+            'GetPrincipal': grpc.unary_unary_rpc_method_handler(
+                    servicer.GetPrincipal,
+                    request_deserializer=object__id__pb2.PrincipalId.FromString,
+                    response_serializer=acls__pb2.Principal.SerializeToString,
+            ),
             'Whoami': grpc.unary_unary_rpc_method_handler(
                     servicer.Whoami,
                     request_deserializer=google_dot_protobuf_dot_empty__pb2.Empty.FromString,
@@ -2582,6 +2598,23 @@ def PutPrincipal(request,
             options, channel_credentials,
             insecure, call_credentials, compression, wait_for_ready, timeout, metadata)
 
+    @staticmethod
+    def GetPrincipal(request,
+            target,
+            options=(),
+            channel_credentials=None,
+            call_credentials=None,
+            insecure=False,
+            compression=None,
+            wait_for_ready=None,
+            timeout=None,
+            metadata=None):
+        return grpc.experimental.unary_unary(request, target, '/littlehorse.LittleHorse/GetPrincipal',
+            object__id__pb2.PrincipalId.SerializeToString,
+            acls__pb2.Principal.FromString,
+            options, channel_credentials,
+            insecure, call_credentials, compression, wait_for_ready, timeout, metadata)
+
     @staticmethod
     def Whoami(request,
             target,
diff --git a/server/src/main/java/io/littlehorse/common/LHServerConfig.java b/server/src/main/java/io/littlehorse/common/LHServerConfig.java
index 399552ee1..ff8835f02 100644
--- a/server/src/main/java/io/littlehorse/common/LHServerConfig.java
+++ b/server/src/main/java/io/littlehorse/common/LHServerConfig.java
@@ -1079,17 +1079,12 @@ public ServerCredentials getInternalServerCreds() {
         String caCertFile = getOrSetDefault(INTERNAL_CA_CERT_KEY, null);
         String serverCertFile = getOrSetDefault(INTERNAL_SERVER_CERT_KEY, null);
         String serverKeyFile = getOrSetDefault(INTERNAL_SERVER_KEY_KEY, null);
-        return getCreds(caCertFile, serverCertFile, serverKeyFile);
-    }
 
-    public ChannelCredentials getInternalClientCreds() {
-        String caCertFile = getOrSetDefault(INTERNAL_CA_CERT_KEY, null);
-        String serverCertFile = getOrSetDefault(INTERNAL_SERVER_CERT_KEY, null);
-        String serverKeyFile = getOrSetDefault(INTERNAL_SERVER_KEY_KEY, null);
         if (caCertFile == null) {
-            log.info("No ca cert file, using plaintext internal client");
+            log.info("No ca cert file found, deploying insecure!");
             return null;
         }
+
         if (serverCertFile == null || serverKeyFile == null) {
             throw new LHMisconfigurationException("CA cert file provided but missing cert or key");
         }
@@ -1098,21 +1093,24 @@ public ChannelCredentials getInternalClientCreds() {
         File rootCA = new File(caCertFile);
 
         try {
-            return TlsChannelCredentials.newBuilder()
+            return TlsServerCredentials.newBuilder()
                     .keyManager(serverCert, serverKey)
                     .trustManager(rootCA)
+                    .clientAuth(TlsServerCredentials.ClientAuth.REQUIRE)
                     .build();
         } catch (IOException exn) {
             throw new RuntimeException(exn);
         }
     }
 
-    private ServerCredentials getCreds(String caCertFile, String serverCertFile, String serverKeyFile) {
+    public ChannelCredentials getInternalClientCreds() {
+        String caCertFile = getOrSetDefault(INTERNAL_CA_CERT_KEY, null);
+        String serverCertFile = getOrSetDefault(INTERNAL_SERVER_CERT_KEY, null);
+        String serverKeyFile = getOrSetDefault(INTERNAL_SERVER_KEY_KEY, null);
         if (caCertFile == null) {
-            log.info("No ca cert file found, deploying insecure!");
+            log.info("No ca cert file, using plaintext internal client");
             return null;
         }
-
         if (serverCertFile == null || serverKeyFile == null) {
             throw new LHMisconfigurationException("CA cert file provided but missing cert or key");
         }
@@ -1121,10 +1119,9 @@ private ServerCredentials getCreds(String caCertFile, String serverCertFile, Str
         File rootCA = new File(caCertFile);
 
         try {
-            return TlsServerCredentials.newBuilder()
+            return TlsChannelCredentials.newBuilder()
                     .keyManager(serverCert, serverKey)
                     .trustManager(rootCA)
-                    .clientAuth(TlsServerCredentials.ClientAuth.REQUIRE)
                     .build();
         } catch (IOException exn) {
             throw new RuntimeException(exn);
diff --git a/server/src/main/java/io/littlehorse/common/model/getable/core/variable/VariableValueModel.java b/server/src/main/java/io/littlehorse/common/model/getable/core/variable/VariableValueModel.java
index ca3053b45..d8c801b41 100644
--- a/server/src/main/java/io/littlehorse/common/model/getable/core/variable/VariableValueModel.java
+++ b/server/src/main/java/io/littlehorse/common/model/getable/core/variable/VariableValueModel.java
@@ -2,7 +2,12 @@
 
 import com.google.protobuf.ByteString;
 import com.google.protobuf.Message;
+import com.jayway.jsonpath.Configuration;
+import com.jayway.jsonpath.DocumentContext;
 import com.jayway.jsonpath.JsonPath;
+import com.jayway.jsonpath.Option;
+import com.jayway.jsonpath.ParseContext;
+import com.jayway.jsonpath.PathNotFoundException;
 import io.littlehorse.common.LHSerializable;
 import io.littlehorse.common.exceptions.LHVarSubError;
 import io.littlehorse.common.util.LHUtil;
@@ -121,7 +126,11 @@ public void updateJsonViaJsonPath(String jsonPath, Object toPut) throws LHVarSub
         String jsonString = getJsonString();
         String newJsonString;
         try {
-            newJsonString = JsonPath.parse(jsonString).set(jsonPath, toPut).jsonString();
+            ParseContext parser =
+                    JsonPath.using(Configuration.defaultConfiguration().addOptions(Option.DEFAULT_PATH_LEAF_TO_NULL));
+            DocumentContext jsonDoc = parser.parse(jsonString);
+
+            newJsonString = jsonDoc.set(jsonPath, toPut).jsonString();
         } catch (Exception jsonExn) {
             throw new LHVarSubError(
                     jsonExn,
@@ -181,25 +190,19 @@ public VariableValueModel getCopy() {
 
     public VariableValueModel operate(
             VariableMutationType operation, VariableValueModel rhs, VariableType typeToCoerceTo) throws LHVarSubError {
-        if (getType() != null) {
-            if (getType() != typeToCoerceTo) {
-                throw new LHVarSubError(
-                        null, "got unexpected variable type. Thought it was a " + typeToCoerceTo + " but is a " + type);
-            }
-        }
 
         if (operation == VariableMutationType.ASSIGN) {
-            if (getType() == null) return rhs.coerceToType(typeToCoerceTo);
-            return rhs.coerceToType(getType());
+            return rhs.coerceToType(typeToCoerceTo);
+        }
 
-        } else if (operation == VariableMutationType.ADD) {
-            return add(rhs);
+        if (operation == VariableMutationType.ADD) {
+            return typeToCoerceTo == VariableType.DOUBLE ? asDouble().add(rhs) : add(rhs);
         } else if (operation == VariableMutationType.SUBTRACT) {
-            return subtract(rhs);
+            return typeToCoerceTo == VariableType.DOUBLE ? asDouble().subtract(rhs) : subtract(rhs);
         } else if (operation == VariableMutationType.MULTIPLY) {
-            return multiply(rhs);
+            return typeToCoerceTo == VariableType.DOUBLE ? asDouble().multiply(rhs) : multiply(rhs);
         } else if (operation == VariableMutationType.DIVIDE) {
-            return divide(rhs);
+            return typeToCoerceTo == VariableType.DOUBLE ? asDouble().divide(rhs) : divide(rhs);
         } else if (operation == VariableMutationType.EXTEND) {
             return extend(rhs);
         } else if (operation == VariableMutationType.REMOVE_IF_PRESENT) {
@@ -230,13 +233,17 @@ public VariableValueModel jsonPath(String path) throws LHVarSubError {
 
         try {
             val = JsonPath.parse(jsonStr).read(path);
+        } catch (PathNotFoundException exn) {
+            return new VariableValueModel();
         } catch (Exception exn) {
+            exn.printStackTrace();
             throw new LHVarSubError(
                     exn, "Failed accessing path " + path + " on data " + jsonStr + "  :\n" + exn.getMessage());
         }
 
         if (val == null) {
-            // TODO: Need to handle this better.
+            // We do not differentiate between the key not being there and the key being explicitly
+            // set to the value of null.
             return new VariableValueModel();
         }
 
@@ -261,7 +268,13 @@ public VariableValueModel jsonPath(String path) throws LHVarSubError {
     }
 
     public VariableValueModel add(VariableValueModel rhs) throws LHVarSubError {
+        if (rhs.getType() == null) {
+            throw new LHVarSubError(null, "Cannot add by null");
+        }
         if (getType() == VariableType.INT) {
+            if (rhs.getType() == VariableType.DOUBLE) {
+                return new VariableValueModel(asDouble().doubleVal + rhs.asDouble().doubleVal);
+            }
             return new VariableValueModel(asInt().intVal + rhs.asInt().intVal);
         } else if (getType() == VariableType.DOUBLE) {
             return new VariableValueModel(asDouble().doubleVal + rhs.asDouble().doubleVal);
@@ -278,7 +291,13 @@ public VariableValueModel add(VariableValueModel rhs) throws LHVarSubError {
     }
 
     public VariableValueModel subtract(VariableValueModel rhs) throws LHVarSubError {
+        if (rhs.getType() == null) {
+            throw new LHVarSubError(null, "Cannot subtract null");
+        }
         if (getType() == VariableType.INT) {
+            if (rhs.getType() == VariableType.DOUBLE) {
+                return new VariableValueModel((long) (asDouble().doubleVal - rhs.asDouble().doubleVal));
+            }
             return new VariableValueModel(asInt().intVal - rhs.asInt().intVal);
         } else if (getType() == VariableType.DOUBLE) {
             return new VariableValueModel(asDouble().doubleVal - rhs.asDouble().doubleVal);
@@ -287,15 +306,29 @@ public VariableValueModel subtract(VariableValueModel rhs) throws LHVarSubError
     }
 
     public VariableValueModel multiply(VariableValueModel rhs) throws LHVarSubError {
+        if (rhs.getType() == null) {
+            throw new LHVarSubError(null, "Cannot multiply by null");
+        }
         if (getType() == VariableType.INT) {
-            return new VariableValueModel((long) (asInt().intVal * rhs.asDouble().doubleVal));
+            if (rhs.getType() == VariableType.DOUBLE) {
+                return new VariableValueModel((long) (asDouble().doubleVal * rhs.asDouble().doubleVal));
+            }
+            return new VariableValueModel((long) (intVal * rhs.asInt().intVal));
         } else if (getType() == VariableType.DOUBLE) {
             return new VariableValueModel((double) (asDouble().doubleVal * rhs.asDouble().doubleVal));
         }
-        throw new LHVarSubError(null, "Cannot multiply var of type " + type);
+        throw new LHVarSubError(null, "Cannot multiply value of type " + type);
     }
 
     public VariableValueModel divide(VariableValueModel rhs) throws LHVarSubError {
+        if (rhs.getType() == null) {
+            throw new LHVarSubError(null, "Cannot divide by null");
+        }
+
+        if (rhs.asDouble().doubleVal == 0) {
+            throw new LHVarSubError(null, "Cannot divide by zero");
+        }
+
         if (getType() == VariableType.INT) {
             if (rhs.getType() == VariableType.DOUBLE) {
                 return new VariableValueModel((long) (asDouble().doubleVal / rhs.asDouble().doubleVal));
@@ -324,6 +357,8 @@ public VariableValueModel extend(VariableValueModel rhs) throws LHVarSubError {
                 throw new LHVarSubError(exn, "Failed concatenating bytes");
             }
             return new VariableValueModel(baos.toByteArray());
+        } else if (getType() == VariableType.STR) {
+            return new VariableValueModel(this.strVal + rhs.asStr().strVal);
         }
         throw new LHVarSubError(null, "Cannot extend var of type " + type);
     }
@@ -423,8 +458,8 @@ public VariableValueModel asInt() throws LHVarSubError {
                 throw new LHVarSubError(exn, "Couldn't convert strVal to INT");
             }
         } else {
-            log.error("Can't convert {} to INT ({})", type, LHUtil.objToString(jsonArrVal));
-            throw new LHVarSubError(null, "Cant convert " + type + " to INT");
+            String typeDescription = type == ValueCase.VALUE_NOT_SET ? "NULL" : type.toString();
+            throw new LHVarSubError(null, "Cant convert " + typeDescription + " to INT");
         }
 
         if (out == null) {
diff --git a/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/ThreadRunModel.java b/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/ThreadRunModel.java
index 8c98f11a5..1ca43cd8c 100644
--- a/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/ThreadRunModel.java
+++ b/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/ThreadRunModel.java
@@ -24,6 +24,7 @@
 import io.littlehorse.common.model.getable.global.wfspec.thread.InterruptDefModel;
 import io.littlehorse.common.model.getable.global.wfspec.thread.ThreadSpecModel;
 import io.littlehorse.common.model.getable.global.wfspec.thread.ThreadVarDefModel;
+import io.littlehorse.common.model.getable.global.wfspec.variable.ExpressionModel;
 import io.littlehorse.common.model.getable.global.wfspec.variable.VariableAssignmentModel;
 import io.littlehorse.common.model.getable.global.wfspec.variable.VariableDefModel;
 import io.littlehorse.common.model.getable.objectId.ExternalEventDefIdModel;
@@ -816,6 +817,10 @@ public VariableValueModel assignVariable(VariableAssignmentModel assn, Map<Strin
                 }
                 val = output.get();
                 break;
+            case EXPRESSION:
+                ExpressionModel expression = assn.getExpression();
+                val = expression.evaluate(varAssn -> assignVariable(varAssn, txnCache));
+                break;
             case SOURCE_NOT_SET:
                 // This should have been caught by the WfSpecModel#validate()
                 throw new IllegalStateException("Invalid WfSpec with un-set VariableAssignment.");
diff --git a/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/VariableAssignerFunc.java b/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/VariableAssignerFunc.java
new file mode 100644
index 000000000..32e5af4de
--- /dev/null
+++ b/server/src/main/java/io/littlehorse/common/model/getable/core/wfrun/VariableAssignerFunc.java
@@ -0,0 +1,9 @@
+package io.littlehorse.common.model.getable.core.wfrun;
+
+import io.littlehorse.common.exceptions.LHVarSubError;
+import io.littlehorse.common.model.getable.core.variable.VariableValueModel;
+import io.littlehorse.common.model.getable.global.wfspec.variable.VariableAssignmentModel;
+
+public interface VariableAssignerFunc {
+    VariableValueModel assign(VariableAssignmentModel varAssn) throws LHVarSubError;
+}
diff --git a/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/ExpressionModel.java b/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/ExpressionModel.java
new file mode 100644
index 000000000..81296b7d6
--- /dev/null
+++ b/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/ExpressionModel.java
@@ -0,0 +1,54 @@
+package io.littlehorse.common.model.getable.global.wfspec.variable;
+
+import com.google.protobuf.Message;
+import io.littlehorse.common.LHSerializable;
+import io.littlehorse.common.exceptions.LHVarSubError;
+import io.littlehorse.common.model.getable.core.variable.VariableValueModel;
+import io.littlehorse.common.model.getable.core.wfrun.VariableAssignerFunc;
+import io.littlehorse.sdk.common.proto.VariableAssignment.Expression;
+import io.littlehorse.sdk.common.proto.VariableMutationType;
+import io.littlehorse.sdk.common.proto.VariableType;
+import io.littlehorse.server.streams.topology.core.ExecutionContext;
+import lombok.Getter;
+
+@Getter
+public class ExpressionModel extends LHSerializable<Expression> {
+
+    private VariableAssignmentModel lhs;
+    private VariableAssignmentModel rhs;
+    private VariableMutationType operation;
+
+    @Override
+    public Class<Expression> getProtoBaseClass() {
+        return Expression.class;
+    }
+
+    @Override
+    public Expression.Builder toProto() {
+        return Expression.newBuilder()
+                .setOperation(operation)
+                .setLhs(lhs.toProto())
+                .setRhs(rhs.toProto());
+    }
+
+    @Override
+    public void initFrom(Message proto, ExecutionContext ignored) {
+        Expression p = (Expression) proto;
+        lhs = LHSerializable.fromProto(p.getLhs(), VariableAssignmentModel.class, ignored);
+        rhs = LHSerializable.fromProto(p.getRhs(), VariableAssignmentModel.class, ignored);
+        operation = p.getOperation();
+    }
+
+    public VariableValueModel evaluate(VariableAssignerFunc variableFinder) throws LHVarSubError {
+        VariableValueModel lhsVal = variableFinder.assign(lhs);
+        VariableValueModel rhsVal = variableFinder.assign(rhs);
+
+        VariableType typeToCoerceTo = lhsVal.getType();
+
+        if (lhsVal.getType() == VariableType.INT && rhsVal.getType() == VariableType.DOUBLE) {
+            typeToCoerceTo = VariableType.DOUBLE;
+        }
+
+        return lhsVal.operate(operation, rhsVal, typeToCoerceTo);
+    }
+}
diff --git a/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableAssignmentModel.java b/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableAssignmentModel.java
index 0de57de7c..f5bf8efe9 100644
--- a/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableAssignmentModel.java
+++ b/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableAssignmentModel.java
@@ -25,6 +25,7 @@ public class VariableAssignmentModel extends LHSerializable<VariableAssignment>
     private VariableValueModel rhsLiteralValue;
     private FormatStringModel formatString;
     private NodeOutputReferenceModel nodeOutputReference;
+    private ExpressionModel expression;
 
     public Class<VariableAssignment> getProtoBaseClass() {
         return VariableAssignment.class;
@@ -50,6 +51,9 @@ public void initFrom(Message proto, ExecutionContext context) {
                 nodeOutputReference =
                         LHSerializable.fromProto(p.getNodeOutput(), NodeOutputReferenceModel.class, context);
                 break;
+            case EXPRESSION:
+                expression = LHSerializable.fromProto(p.getExpression(), ExpressionModel.class, context);
+                break;
             case SOURCE_NOT_SET:
                 // nothing to do;
         }
@@ -73,6 +77,9 @@ public VariableAssignment.Builder toProto() {
             case NODE_OUTPUT:
                 out.setNodeOutput(nodeOutputReference.toProto());
                 break;
+            case EXPRESSION:
+                out.setExpression(expression.toProto());
+                break;
             case SOURCE_NOT_SET:
                 // not possible.
         }
@@ -118,21 +125,19 @@ public boolean canBeType(VariableType type, ThreadSpecModel tspec) {
                 baseType = VariableType.STR;
                 break;
             case NODE_OUTPUT:
+            case EXPRESSION:
                 // TODO (#1124): look at the node to determine if the output of the node
                 // can be a given type.
                 return true;
             case SOURCE_NOT_SET:
-        }
-
-        if (rhsSourceType == null) {
-            // Poorly behaved clients (i.e. someone building a WfSpec by hand) could pass in
-            // protobuf that does not set the source type. Instead of throwing an IllegalStateException
-            // we should throw an error that will get propagated back to the client.
-            //
-            // The problem with this is that in this scope we lack context about which node has the
-            // invalid VariableAssignment, so the client may have trouble determining the source. Still
-            // it is better to return INVALID_ARGUMENT than INTERNAL.
-            throw new LHApiException(Status.INVALID_ARGUMENT, "VariableAssignment passed with missing source");
+                // Poorly behaved clients (i.e. someone building a WfSpec by hand) could pass in
+                // protobuf that does not set the source type. Instead of throwing an IllegalStateException
+                // we should throw an error that will get propagated back to the client.
+                //
+                // The problem with this is that in this scope we lack context about which node has the
+                // invalid VariableAssignment, so the client may have trouble determining the source. Still
+                // it is better to return INVALID_ARGUMENT than INTERNAL.
+                throw new LHApiException(Status.INVALID_ARGUMENT, "VariableAssignment passed with missing source");
         }
 
         return baseType == type;
diff --git a/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableMutationModel.java b/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableMutationModel.java
index 6a09ca48b..264cbd0f9 100644
--- a/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableMutationModel.java
+++ b/server/src/main/java/io/littlehorse/common/model/getable/global/wfspec/variable/VariableMutationModel.java
@@ -142,7 +142,12 @@ public void execute(ThreadRunModel thread, Map<String, VariableValueModel> txnCa
             if (lhsJsonPath != null) {
                 VariableValueModel lhsJsonPathed = lhsVal.jsonPath(lhsJsonPath);
                 VariableType typeToCoerceTo = lhsJsonPathed.getType();
-                VariableValueModel thingToPut = lhsJsonPathed.operate(operation, rhsVal, typeToCoerceTo);
+
+                // If the key does not exist in the LHS, we just plop the RHS there. Otherwise, we want to coerce the
+                // type to the rhs.
+                VariableValueModel thingToPut = lhsJsonPathed.getType() == null
+                        ? rhsVal
+                        : lhsJsonPathed.operate(operation, rhsVal, typeToCoerceTo);
 
                 VariableValueModel currentLhs = getVarValFromThreadInTxn(lhsName, thread, txnCache);
 
diff --git a/server/src/main/java/io/littlehorse/server/LHServer.java b/server/src/main/java/io/littlehorse/server/LHServer.java
index fc7760a40..a72af4adf 100644
--- a/server/src/main/java/io/littlehorse/server/LHServer.java
+++ b/server/src/main/java/io/littlehorse/server/LHServer.java
@@ -20,9 +20,8 @@
 import io.littlehorse.sdk.common.exception.LHMisconfigurationException;
 import io.littlehorse.sdk.common.proto.LHHostInfo;
 import io.littlehorse.sdk.common.proto.PollTaskResponse;
-import io.littlehorse.server.auth.InternalCallCredentials;
 import io.littlehorse.server.auth.RequestAuthorizer;
-import io.littlehorse.server.auth.RequestSanitizer;
+import io.littlehorse.server.auth.internalport.InternalCallCredentials;
 import io.littlehorse.server.listener.ServerListenerConfig;
 import io.littlehorse.server.monitoring.HealthService;
 import io.littlehorse.server.streams.BackendInternalComms;
@@ -122,8 +121,7 @@ private LHServerListener createListener(ServerListenerConfig listenerConfig) {
                 List.of(
                         new MetricCollectingServerInterceptor(healthService.getMeterRegistry()),
                         new RequestAuthorizer(contextKey, metadataCache, coreStoreProvider, config),
-                        listenerConfig.getServerAuthorizer(),
-                        new RequestSanitizer()),
+                        listenerConfig.getRequestAuthenticator()),
                 contextKey);
     }
 
diff --git a/server/src/main/java/io/littlehorse/server/LHServerListener.java b/server/src/main/java/io/littlehorse/server/LHServerListener.java
index 85e3fb3bd..c344c4400 100644
--- a/server/src/main/java/io/littlehorse/server/LHServerListener.java
+++ b/server/src/main/java/io/littlehorse/server/LHServerListener.java
@@ -126,6 +126,7 @@
 import io.littlehorse.sdk.common.proto.PollTaskRequest;
 import io.littlehorse.sdk.common.proto.PollTaskResponse;
 import io.littlehorse.sdk.common.proto.Principal;
+import io.littlehorse.sdk.common.proto.PrincipalId;
 import io.littlehorse.sdk.common.proto.PrincipalIdList;
 import io.littlehorse.sdk.common.proto.PutExternalEventDefRequest;
 import io.littlehorse.sdk.common.proto.PutExternalEventRequest;
@@ -199,7 +200,7 @@
 import io.littlehorse.sdk.common.proto.WorkflowEventId;
 import io.littlehorse.sdk.common.proto.WorkflowEventIdList;
 import io.littlehorse.sdk.common.proto.WorkflowEventList;
-import io.littlehorse.server.auth.InternalCallCredentials;
+import io.littlehorse.server.auth.internalport.InternalCallCredentials;
 import io.littlehorse.server.listener.ServerListenerConfig;
 import io.littlehorse.server.streams.BackendInternalComms;
 import io.littlehorse.server.streams.lhinternalscan.PublicScanReply;
@@ -1046,6 +1047,23 @@ public void getTenant(TenantId req, StreamObserver<Tenant> ctx) {
         ctx.onCompleted();
     }
 
+    @Override
+    @Authorize(
+            resources = {ACLResource.ACL_PRINCIPAL},
+            actions = ACLAction.READ)
+    public void getPrincipal(PrincipalId req, StreamObserver<Principal> ctx) {
+        RequestExecutionContext reqContext = requestContext();
+        PrincipalIdModel principalId = PrincipalIdModel.fromProto(req, PrincipalIdModel.class, reqContext);
+        PrincipalModel result = reqContext
+                .metadataManager()
+                .getOrThrow(
+                        principalId,
+                        () -> new LHApiException(
+                                Status.NOT_FOUND, "Could not find Principal %s".formatted(principalId)));
+        ctx.onNext(result.toProto().build());
+        ctx.onCompleted();
+    }
+
     @Override
     @Authorize(
             resources = {},
diff --git a/server/src/main/java/io/littlehorse/server/auth/InsecureServerAuthorizer.java b/server/src/main/java/io/littlehorse/server/auth/InsecureServerAuthorizer.java
deleted file mode 100644
index 035fb2059..000000000
--- a/server/src/main/java/io/littlehorse/server/auth/InsecureServerAuthorizer.java
+++ /dev/null
@@ -1,19 +0,0 @@
-package io.littlehorse.server.auth;
-
-import io.grpc.Metadata;
-import io.grpc.ServerCall;
-import io.grpc.ServerCall.Listener;
-import io.grpc.ServerCallHandler;
-
-public class InsecureServerAuthorizer implements ServerAuthorizer {
-
-    @Override
-    public <ReqT, RespT> Listener<ReqT> interceptCall(
-            ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
-        return next.startCall(call, headers);
-    }
-
-    public static InsecureServerAuthorizer create() {
-        return new InsecureServerAuthorizer();
-    }
-}
diff --git a/server/src/main/java/io/littlehorse/server/auth/ServerAuthorizer.java b/server/src/main/java/io/littlehorse/server/auth/LHServerInterceptor.java
similarity index 65%
rename from server/src/main/java/io/littlehorse/server/auth/ServerAuthorizer.java
rename to server/src/main/java/io/littlehorse/server/auth/LHServerInterceptor.java
index 1fe9df634..cff92fda3 100644
--- a/server/src/main/java/io/littlehorse/server/auth/ServerAuthorizer.java
+++ b/server/src/main/java/io/littlehorse/server/auth/LHServerInterceptor.java
@@ -4,7 +4,12 @@
 import io.grpc.ServerInterceptor;
 import io.littlehorse.common.LHConstants;
 
-public interface ServerAuthorizer extends ServerInterceptor {
+/**
+ * Wrapper over io.grpc.ServerInterceptor. Doesn't do anything other than put
+ * a few constants into scope without imports in order to reduce the scope of
+ * how we expose the `Metadata.Key` stuff.
+ */
+public interface LHServerInterceptor extends ServerInterceptor {
 
     String INTERNAL_PREFIX = "_";
 
diff --git a/server/src/main/java/io/littlehorse/server/auth/MTLSServerAuthorizer.java b/server/src/main/java/io/littlehorse/server/auth/MTLSServerAuthorizer.java
deleted file mode 100644
index 4ebd86e47..000000000
--- a/server/src/main/java/io/littlehorse/server/auth/MTLSServerAuthorizer.java
+++ /dev/null
@@ -1,29 +0,0 @@
-package io.littlehorse.server.auth;
-
-import io.grpc.Metadata;
-import io.grpc.ServerCall;
-import io.grpc.ServerCall.Listener;
-import io.grpc.ServerCallHandler;
-import io.littlehorse.common.util.CertificateUtil;
-import io.littlehorse.server.listener.MTLSConfig;
-
-public class MTLSServerAuthorizer implements ServerAuthorizer {
-
-    private final String commonName;
-
-    public MTLSServerAuthorizer(MTLSConfig mtlsConfig) {
-        try {
-            this.commonName = CertificateUtil.getCommonNameFromCertificate(mtlsConfig.getCaCertificate());
-        } catch (Exception ex) {
-            throw new IllegalArgumentException("Certificate is not valid", ex);
-        }
-    }
-
-    @Override
-    public <ReqT, RespT> Listener<ReqT> interceptCall(
-            ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
-        headers.put(CLIENT_ID, this.commonName);
-
-        return next.startCall(call, headers);
-    }
-}
diff --git a/server/src/main/java/io/littlehorse/server/auth/RequestAuthorizer.java b/server/src/main/java/io/littlehorse/server/auth/RequestAuthorizer.java
index 06a46574e..dfda3d720 100644
--- a/server/src/main/java/io/littlehorse/server/auth/RequestAuthorizer.java
+++ b/server/src/main/java/io/littlehorse/server/auth/RequestAuthorizer.java
@@ -32,7 +32,7 @@
 import lombok.extern.slf4j.Slf4j;
 
 @Slf4j
-public class RequestAuthorizer implements ServerAuthorizer {
+public class RequestAuthorizer implements LHServerInterceptor {
 
     private final CoreStoreProvider coreStoreProvider;
 
diff --git a/server/src/main/java/io/littlehorse/server/auth/RequestSanitizer.java b/server/src/main/java/io/littlehorse/server/auth/RequestSanitizer.java
deleted file mode 100644
index bc1c5d903..000000000
--- a/server/src/main/java/io/littlehorse/server/auth/RequestSanitizer.java
+++ /dev/null
@@ -1,18 +0,0 @@
-package io.littlehorse.server.auth;
-
-import io.grpc.Context;
-import io.grpc.Contexts;
-import io.grpc.Metadata;
-import io.grpc.ServerCall;
-import io.grpc.ServerCallHandler;
-
-public class RequestSanitizer implements ServerAuthorizer {
-
-    @Override
-    public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
-            ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
-        Context context = Context.current();
-        headers.discardAll(CLIENT_ID);
-        return Contexts.interceptCall(context, call, headers, next);
-    }
-}
diff --git a/server/src/main/java/io/littlehorse/server/auth/authenticators/InsecureAuthenticator.java b/server/src/main/java/io/littlehorse/server/auth/authenticators/InsecureAuthenticator.java
new file mode 100644
index 000000000..2a884ea27
--- /dev/null
+++ b/server/src/main/java/io/littlehorse/server/auth/authenticators/InsecureAuthenticator.java
@@ -0,0 +1,26 @@
+package io.littlehorse.server.auth.authenticators;
+
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.ServerCall.Listener;
+import io.grpc.ServerCallHandler;
+import io.littlehorse.common.LHConstants;
+import io.littlehorse.server.auth.LHServerInterceptor;
+
+/**
+ * Authenticator for insecure server listeners. Sets the principal id to `anonymous` for all requests.
+ */
+public class InsecureAuthenticator implements LHServerInterceptor {
+
+    @Override
+    public <ReqT, RespT> Listener<ReqT> interceptCall(
+            ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
+
+        headers.put(CLIENT_ID, LHConstants.ANONYMOUS_PRINCIPAL);
+        return next.startCall(call, headers);
+    }
+
+    public static InsecureAuthenticator create() {
+        return new InsecureAuthenticator();
+    }
+}
diff --git a/server/src/main/java/io/littlehorse/server/auth/authenticators/MTLSAuthenticator.java b/server/src/main/java/io/littlehorse/server/auth/authenticators/MTLSAuthenticator.java
new file mode 100644
index 000000000..df51dab2e
--- /dev/null
+++ b/server/src/main/java/io/littlehorse/server/auth/authenticators/MTLSAuthenticator.java
@@ -0,0 +1,73 @@
+package io.littlehorse.server.auth.authenticators;
+
+import io.grpc.Grpc;
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.ServerCall.Listener;
+import io.grpc.ServerCallHandler;
+import io.grpc.Status;
+import io.littlehorse.common.LHConstants;
+import io.littlehorse.server.auth.LHServerInterceptor;
+import java.security.Principal;
+import java.util.List;
+import javax.naming.InvalidNameException;
+import javax.naming.ldap.LdapName;
+import javax.naming.ldap.Rdn;
+import javax.net.ssl.SSLPeerUnverifiedException;
+import javax.net.ssl.SSLSession;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * Authenticator for requests on MTLS listeners. Sets the principal id to the common name of the client
+ * certificate.
+ */
+@Slf4j
+public class MTLSAuthenticator implements LHServerInterceptor {
+
+    @Override
+    public <ReqT, RespT> Listener<ReqT> interceptCall(
+            ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
+
+        SSLSession clientTlsInfo = call.getAttributes().get(Grpc.TRANSPORT_ATTR_SSL_SESSION);
+
+        if (clientTlsInfo == null) {
+            throw new IllegalStateException(
+                    "MTLSAuthenticator should only be used on MTLS ports, so SSLSession should be present");
+        }
+
+        String commonName;
+        try {
+            // Determine commonName from the client certificate
+            Principal peerPrincipal = clientTlsInfo.getPeerPrincipal(); // NOT a littlehorse Principal
+
+            LdapName ln = new LdapName(peerPrincipal.getName());
+
+            List<String> commonNames = ln.getRdns().stream()
+                    .filter(rdn -> rdn.getType().equalsIgnoreCase("CN"))
+                    .map(Rdn::getValue)
+                    .map(Object::toString)
+                    .toList();
+
+            if (commonNames.size() == 0) {
+                // This happens when the client certificate does not have a CommonName.
+                // Note that the interceptor wouldn't even be called if the SSL handshake failed,
+                // so we know at this point that the client presented a valid certificate.
+                //
+                // Since they did not set a commonName on the certificate, we treat them as
+                // anonymous.
+                commonName = LHConstants.ANONYMOUS_PRINCIPAL;
+            } else {
+                commonName = commonNames.get(0);
+            }
+
+            headers.put(CLIENT_ID, commonName);
+            log.trace("Got common name from client certificate: {}", commonName);
+            return next.startCall(call, headers);
+        } catch (InvalidNameException | SSLPeerUnverifiedException e) {
+            // close the call as unauthenticated
+            log.trace("Closing the call as unauthenticated due to certiciate exception", e);
+            call.close(Status.UNAUTHENTICATED.withDescription("Invalid certificate"), new Metadata());
+            return new ServerCall.Listener<>() {};
+        }
+    }
+}
diff --git a/server/src/main/java/io/littlehorse/server/auth/OAuthServerAuthenticator.java b/server/src/main/java/io/littlehorse/server/auth/authenticators/OAuthAuthenticator.java
similarity index 89%
rename from server/src/main/java/io/littlehorse/server/auth/OAuthServerAuthenticator.java
rename to server/src/main/java/io/littlehorse/server/auth/authenticators/OAuthAuthenticator.java
index c1c231fa0..ac6def30a 100644
--- a/server/src/main/java/io/littlehorse/server/auth/OAuthServerAuthenticator.java
+++ b/server/src/main/java/io/littlehorse/server/auth/authenticators/OAuthAuthenticator.java
@@ -1,4 +1,4 @@
-package io.littlehorse.server.auth;
+package io.littlehorse.server.auth.authenticators;
 
 import com.google.common.base.Strings;
 import com.google.common.cache.Cache;
@@ -10,16 +10,21 @@
 import io.grpc.ServerCallHandler;
 import io.grpc.Status;
 import io.littlehorse.sdk.common.auth.TokenStatus;
+import io.littlehorse.server.auth.LHServerInterceptor;
+import io.littlehorse.server.auth.OAuthConfig;
+import io.littlehorse.server.auth.UnauthenticatedException;
 import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import lombok.extern.slf4j.Slf4j;
 
 /**
+ * Determines the Principal ID from the OAuth token.
+ *
  * Example:
  * https://github.com/grpc/grpc-java/blob/master/examples/example-oauth/src/main/java/io/grpc/examples/oauth/OAuth2ServerInterceptor.java
  */
 @Slf4j
-public class OAuthServerAuthenticator implements ServerAuthorizer {
+public class OAuthAuthenticator implements LHServerInterceptor {
 
     private static final Metadata.Key<String> AUTHORIZATION_HEADER_KEY =
             Metadata.Key.of("Authorization", Metadata.ASCII_STRING_MARSHALLER);
@@ -31,7 +36,7 @@ public class OAuthServerAuthenticator implements ServerAuthorizer {
 
     private final OAuthClient client;
 
-    public OAuthServerAuthenticator(OAuthConfig config) {
+    public OAuthAuthenticator(OAuthConfig config) {
         this.client = new OAuthClient(config);
     }
 
diff --git a/server/src/main/java/io/littlehorse/server/auth/OAuthClient.java b/server/src/main/java/io/littlehorse/server/auth/authenticators/OAuthClient.java
similarity index 95%
rename from server/src/main/java/io/littlehorse/server/auth/OAuthClient.java
rename to server/src/main/java/io/littlehorse/server/auth/authenticators/OAuthClient.java
index 58cd814a6..cec2216b2 100644
--- a/server/src/main/java/io/littlehorse/server/auth/OAuthClient.java
+++ b/server/src/main/java/io/littlehorse/server/auth/authenticators/OAuthClient.java
@@ -1,4 +1,4 @@
-package io.littlehorse.server.auth;
+package io.littlehorse.server.auth.authenticators;
 
 import com.nimbusds.oauth2.sdk.ParseException;
 import com.nimbusds.oauth2.sdk.Scope;
@@ -13,6 +13,8 @@
 import com.nimbusds.openid.connect.sdk.OIDCScopeValue;
 import io.littlehorse.sdk.common.auth.TokenStatus;
 import io.littlehorse.sdk.common.exception.EntityProviderException;
+import io.littlehorse.server.auth.OAuthConfig;
+import io.littlehorse.server.auth.UnauthenticatedException;
 import java.io.IOException;
 import java.time.Instant;
 import lombok.extern.slf4j.Slf4j;
diff --git a/server/src/main/java/io/littlehorse/server/auth/InternalAuthorizer.java b/server/src/main/java/io/littlehorse/server/auth/internalport/InternalAuthorizer.java
similarity index 82%
rename from server/src/main/java/io/littlehorse/server/auth/InternalAuthorizer.java
rename to server/src/main/java/io/littlehorse/server/auth/internalport/InternalAuthorizer.java
index 93257fe3d..703676549 100644
--- a/server/src/main/java/io/littlehorse/server/auth/InternalAuthorizer.java
+++ b/server/src/main/java/io/littlehorse/server/auth/internalport/InternalAuthorizer.java
@@ -1,4 +1,4 @@
-package io.littlehorse.server.auth;
+package io.littlehorse.server.auth.internalport;
 
 import io.grpc.Context;
 import io.grpc.Contexts;
@@ -9,12 +9,20 @@
 import io.littlehorse.common.model.getable.ObjectIdModel;
 import io.littlehorse.common.model.getable.objectId.PrincipalIdModel;
 import io.littlehorse.common.model.getable.objectId.TenantIdModel;
+import io.littlehorse.server.auth.LHServerInterceptor;
 import io.littlehorse.server.streams.topology.core.CoreStoreProvider;
 import io.littlehorse.server.streams.topology.core.RequestExecutionContext;
 import io.littlehorse.server.streams.util.MetadataCache;
 import java.util.Objects;
 
-public class InternalAuthorizer implements ServerAuthorizer {
+/**
+ * ServerInterceptor to populate the RequestExecutionContext with the TenantId and PrincipalId
+ * for interactive queries between LH Servers.
+ *
+ * While the request is technically made from one LH Server to another, we want the receiving
+ * server to treat it as if it were made by the original client.
+ */
+public class InternalAuthorizer implements LHServerInterceptor {
 
     private final Context.Key<RequestExecutionContext> executionContextKey;
     private final CoreStoreProvider coreStoreProvider;
diff --git a/server/src/main/java/io/littlehorse/server/auth/InternalCallCredentials.java b/server/src/main/java/io/littlehorse/server/auth/internalport/InternalCallCredentials.java
similarity index 85%
rename from server/src/main/java/io/littlehorse/server/auth/InternalCallCredentials.java
rename to server/src/main/java/io/littlehorse/server/auth/internalport/InternalCallCredentials.java
index 941a8e85a..fb118366a 100644
--- a/server/src/main/java/io/littlehorse/server/auth/InternalCallCredentials.java
+++ b/server/src/main/java/io/littlehorse/server/auth/internalport/InternalCallCredentials.java
@@ -1,14 +1,20 @@
-package io.littlehorse.server.auth;
+package io.littlehorse.server.auth.internalport;
 
 import io.grpc.CallCredentials;
 import io.grpc.Metadata;
 import io.grpc.Status;
 import io.littlehorse.common.AuthorizationContext;
+import io.littlehorse.server.auth.RequestAuthorizer;
 import io.littlehorse.server.streams.topology.core.BackgroundContext;
 import io.littlehorse.server.streams.topology.core.ProcessorExecutionContext;
 import io.littlehorse.server.streams.topology.core.RequestExecutionContext;
 import java.util.concurrent.Executor;
 
+/**
+ * Call Credentials that allows the LH Server to propagate information about the calling Tenant
+ * and Principal when making an Interactive Query between two different LH Servers on the
+ * internal port.
+ */
 public class InternalCallCredentials extends CallCredentials {
     private final AuthorizationContext currentAuthorization;
 
diff --git a/server/src/main/java/io/littlehorse/server/listener/ServerListenerConfig.java b/server/src/main/java/io/littlehorse/server/listener/ServerListenerConfig.java
index d1aa0bf25..2279bd818 100644
--- a/server/src/main/java/io/littlehorse/server/listener/ServerListenerConfig.java
+++ b/server/src/main/java/io/littlehorse/server/listener/ServerListenerConfig.java
@@ -6,10 +6,10 @@
 import io.grpc.TlsServerCredentials;
 import io.littlehorse.common.LHServerConfig;
 import io.littlehorse.server.auth.AuthorizationProtocol;
-import io.littlehorse.server.auth.InsecureServerAuthorizer;
-import io.littlehorse.server.auth.MTLSServerAuthorizer;
-import io.littlehorse.server.auth.OAuthServerAuthenticator;
-import io.littlehorse.server.auth.ServerAuthorizer;
+import io.littlehorse.server.auth.LHServerInterceptor;
+import io.littlehorse.server.auth.authenticators.InsecureAuthenticator;
+import io.littlehorse.server.auth.authenticators.MTLSAuthenticator;
+import io.littlehorse.server.auth.authenticators.OAuthAuthenticator;
 import java.io.IOException;
 import lombok.Builder;
 import lombok.Getter;
@@ -67,11 +67,11 @@ public ServerCredentials getCredentials() {
         }
     }
 
-    public ServerAuthorizer getServerAuthorizer() {
+    public LHServerInterceptor getRequestAuthenticator() {
         return switch (authorizationProtocol) {
-            case OAUTH -> new OAuthServerAuthenticator(config.getOAuthConfig());
-            case MTLS -> new MTLSServerAuthorizer(config.getMTLSConfiguration(name));
-            default -> InsecureServerAuthorizer.create();
+            case OAUTH -> new OAuthAuthenticator(config.getOAuthConfig());
+            case MTLS -> new MTLSAuthenticator();
+            default -> InsecureAuthenticator.create();
         };
     }
 }
diff --git a/server/src/main/java/io/littlehorse/server/streams/BackendInternalComms.java b/server/src/main/java/io/littlehorse/server/streams/BackendInternalComms.java
index 075002398..402d58989 100644
--- a/server/src/main/java/io/littlehorse/server/streams/BackendInternalComms.java
+++ b/server/src/main/java/io/littlehorse/server/streams/BackendInternalComms.java
@@ -53,8 +53,8 @@
 import io.littlehorse.sdk.common.proto.LHHostInfo;
 import io.littlehorse.sdk.common.proto.WorkflowEvent;
 import io.littlehorse.server.GlobalExceptionHandler;
-import io.littlehorse.server.auth.InternalAuthorizer;
-import io.littlehorse.server.auth.InternalCallCredentials;
+import io.littlehorse.server.auth.internalport.InternalAuthorizer;
+import io.littlehorse.server.auth.internalport.InternalCallCredentials;
 import io.littlehorse.server.listener.AdvertisedListenerConfig;
 import io.littlehorse.server.streams.lhinternalscan.InternalScan;
 import io.littlehorse.server.streams.lhinternalscan.publicrequests.scanfilter.ScanFilterModel;
diff --git a/server/src/main/java/io/littlehorse/server/streams/topology/core/ProcessorExecutionContext.java b/server/src/main/java/io/littlehorse/server/streams/topology/core/ProcessorExecutionContext.java
index 07a540b80..07b283a73 100644
--- a/server/src/main/java/io/littlehorse/server/streams/topology/core/ProcessorExecutionContext.java
+++ b/server/src/main/java/io/littlehorse/server/streams/topology/core/ProcessorExecutionContext.java
@@ -12,7 +12,7 @@
 import io.littlehorse.common.proto.Command;
 import io.littlehorse.sdk.common.proto.LHHostInfo;
 import io.littlehorse.server.LHServer;
-import io.littlehorse.server.auth.InternalCallCredentials;
+import io.littlehorse.server.auth.internalport.InternalCallCredentials;
 import io.littlehorse.server.streams.ServerTopology;
 import io.littlehorse.server.streams.storeinternals.GetableManager;
 import io.littlehorse.server.streams.storeinternals.ReadOnlyMetadataManager;
diff --git a/server/src/test/java/e2e/ExpressionTest.java b/server/src/test/java/e2e/ExpressionTest.java
new file mode 100644
index 000000000..13f5b5117
--- /dev/null
+++ b/server/src/test/java/e2e/ExpressionTest.java
@@ -0,0 +1,314 @@
+package e2e;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.littlehorse.sdk.common.proto.Failure;
+import io.littlehorse.sdk.common.proto.LHErrorType;
+import io.littlehorse.sdk.common.proto.LHStatus;
+import io.littlehorse.sdk.common.util.Arg;
+import io.littlehorse.sdk.wfsdk.LHExpression;
+import io.littlehorse.sdk.wfsdk.Workflow;
+import io.littlehorse.sdk.wfsdk.internal.WorkflowImpl;
+import io.littlehorse.sdk.worker.LHTaskMethod;
+import io.littlehorse.test.LHTest;
+import io.littlehorse.test.LHWorkflow;
+import io.littlehorse.test.WorkflowVerifier;
+import java.util.Map;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+@LHTest
+public class ExpressionTest {
+
+    @LHWorkflow("basic-expression-manipulation")
+    private Workflow expressionWf;
+
+    private WorkflowVerifier verifier;
+
+    @Test
+    public void shouldExtendString() {
+        verifier.prepareRun(expressionWf, Arg.of("my-str", "hello"))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "my-str", variable -> {
+                    Assertions.assertEquals("hello-suffix", variable.getStr());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldAddIntAndIgnoreLHSWhenAssigning() {
+        verifier.prepareRun(expressionWf, Arg.of("int-to-add", 1), Arg.of("int-to-add-result", 137))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "int-to-add-result", variable -> {
+                    Assertions.assertEquals(3, variable.getInt());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldNotChangeVariableUsedInExpression() {
+        verifier.prepareRun(expressionWf, Arg.of("int-to-add", 1))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "int-to-add", variable -> {
+                    Assertions.assertEquals(1, variable.getInt());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldAddIntAndAssignToNullVariable() {
+        verifier.prepareRun(expressionWf, Arg.of("int-to-add", 1))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "int-to-add-result", variable -> {
+                    Assertions.assertEquals(3, variable.getInt());
+                })
+                .start();
+    }
+
+    @Test
+    void dividingByZeroThrowsVarSubError() {
+        verifier.prepareRun(expressionWf, Arg.of("thing-to-divide-by-zero", 1))
+                .waitForStatus(LHStatus.ERROR)
+                .thenVerifyLastNodeRun(0, nodeRun -> {
+                    // TODO: Issue #1083 will allow us to uncomment this assertion.
+                    // Assertions.assertEquals(LHStatus.ERROR, nodeRun.getStatus());
+                    Failure mathTest = nodeRun.getFailures(0);
+                    Assertions.assertEquals(mathTest.getFailureName(), LHErrorType.VAR_SUB_ERROR.toString());
+                    Assertions.assertTrue(mathTest.getMessage().toLowerCase().contains("divide by zero"));
+                })
+                .start();
+    }
+
+    @Test
+    void dividingTwoIntsShouldUseIntegerDivision() {
+        verifier.prepareRun(expressionWf, Arg.of("dividend-tests", Map.of("lhs", 5, "rhs", 2)))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "division-result", variable -> {
+                    Assertions.assertEquals(2.0, variable.getDouble());
+                })
+                .start();
+    }
+
+    @Test
+    void dividingDoubleByIntShouldUseFloatingDivision() {
+        verifier.prepareRun(expressionWf, Arg.of("dividend-tests", Map.of("lhs", 5.0, "rhs", 2)))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "division-result", variable -> {
+                    Assertions.assertEquals(2.5, variable.getDouble());
+                })
+                .start();
+    }
+
+    @Test
+    void dividingIntByDoubleShouldUseFloatingDivision() {
+        verifier.prepareRun(expressionWf, Arg.of("dividend-tests", Map.of("lhs", 5, "rhs", 2.0)))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "division-result", variable -> {
+                    Assertions.assertEquals(2.5, variable.getDouble());
+                })
+                .start();
+    }
+
+    @Test
+    void dividingTwoDoublesShouldUseFloatingDivision() {
+        verifier.prepareRun(expressionWf, Arg.of("dividend-tests", Map.of("lhs", 5.0, "rhs", 2.0)))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "division-result", variable -> {
+                    Assertions.assertEquals(2.5, variable.getDouble());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldCastDoubleToIntWhenAssigningToInt() {
+        verifier.prepareRun(expressionWf, Arg.of("dividend-tests", Map.of("lhs", 5.0, "rhs", 2.0)))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "division-result-int", variable -> {
+                    Assertions.assertEquals(2, variable.getInt());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldGetVarSubErrorMultiplyingNull() {
+        verifier.prepareRun(
+                        expressionWf, Arg.of("quantity", 5), Arg.of("price", 2.5), Arg.of("discount-percentage", null))
+                .waitForStatus(LHStatus.ERROR)
+                .thenVerifyLastNodeRun(0, nodeRun -> {
+                    // TODO: Issue #1083 will allow us to uncomment this assertion.
+                    // Assertions.assertEquals(LHStatus.ERROR, nodeRun.getStatus());
+                    Failure mathTest = nodeRun.getFailures(0);
+                    Assertions.assertEquals(mathTest.getFailureName(), LHErrorType.VAR_SUB_ERROR.toString());
+                    Assertions.assertTrue(mathTest.getMessage().toLowerCase().contains("value_not_set")
+                            || mathTest.getMessage().toLowerCase().contains("null"));
+                })
+                .start();
+    }
+
+    @Test
+    void shouldCalculateDiscountProperly() {
+        verifier.prepareRun(
+                        expressionWf, Arg.of("quantity", 10), Arg.of("price", 100.3), Arg.of("discount-percentage", 10))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "total-price-double", variable -> {
+                    Assertions.assertEquals(902.7, variable.getDouble());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldStillUseDoublePrecisionWhenCalculatingBeforeAssigningToAnInt() {
+        verifier.prepareRun(
+                        expressionWf, Arg.of("quantity", 10), Arg.of("price", 100.3), Arg.of("discount-percentage", 10))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "total-price-int", variable -> {
+                    Assertions.assertEquals(902, variable.getInt());
+                })
+                .start();
+    }
+
+    @Test
+    void shouldOverwriteJsonValueWhenMutating() {
+        verifier.prepareRun(expressionWf, Arg.of("json", Map.of("foo", "baz")))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "json", variable -> {
+                    String jsonStr = variable.getJsonObj();
+                    try {
+                        @SuppressWarnings("unchecked")
+                        Map<String, Object> jsonMap = new ObjectMapper().readValue(jsonStr, Map.class);
+                        Assertions.assertEquals("bar", jsonMap.get("foo"));
+                    } catch (JsonProcessingException exn) {
+                        throw new RuntimeException(exn);
+                    }
+                })
+                .start();
+    }
+
+    @Test
+    void shouldAddKeyIfNotExists() {
+        verifier.prepareRun(expressionWf, Arg.of("json", Map.of()))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "json", variable -> {
+                    String jsonStr = variable.getJsonObj();
+                    try {
+                        @SuppressWarnings("unchecked")
+                        Map<String, Object> jsonMap = new ObjectMapper().readValue(jsonStr, Map.class);
+                        Assertions.assertEquals("bar", jsonMap.get("foo"));
+                    } catch (JsonProcessingException exn) {
+                        throw new RuntimeException(exn);
+                    }
+                })
+                .start();
+    }
+
+    @Test
+    void shouldThrowOnSecondLayerNullNestedField() {
+        verifier.prepareRun(expressionWf, Arg.of("nested-json", Map.of()))
+                .waitForStatus(LHStatus.ERROR)
+                .thenVerifyLastNodeRun(0, nodeRun -> {
+                    System.out.println(nodeRun.getFailures(0).getMessage());
+                    Assertions.assertTrue(
+                            nodeRun.getFailures(0).getMessage().toLowerCase().contains("missing property"));
+                })
+                .start();
+    }
+
+    @Test
+    void shouldSetNullNestedFieldWhenFirstLayerProvided() {
+        verifier.prepareRun(expressionWf, Arg.of("nested-json", Map.of("foo", Map.of())))
+                .waitForStatus(LHStatus.COMPLETED)
+                .thenVerifyVariable(0, "nested-json", variable -> {
+                    String jsonStr = variable.getJsonObj();
+                    try {
+                        @SuppressWarnings("unchecked")
+                        Map<String, Object> jsonMap = new ObjectMapper().readValue(jsonStr, Map.class);
+                        Map<String, String> fooMap = (Map<String, String>) jsonMap.get("foo");
+                        Assertions.assertEquals("baz", fooMap.get("bar"));
+                    } catch (JsonProcessingException exn) {
+                        throw new RuntimeException(exn);
+                    }
+                })
+                .start();
+    }
+
+    /*
+     * Each of the tests in here *could* be their own Workflow; however, registering a
+     * workflow takes ~200ms in our testing. Each of these test cases takes about 15ms
+     * to run because it doesn't involve executing a TaskRun. Therefore, even though
+     * it is less clean to have everything in one workflow, we can still achieve many
+     * test cases while adding less than one second to our pipeline.
+     *
+     * Additionally, we have an individual @Test case for each of the logical test cases;
+     * the only difference is that they all share the same WfSpec.
+     */
+    @LHWorkflow("basic-expression-manipulation")
+    public Workflow getExpression() {
+        return new WorkflowImpl("test-expression", wf -> {
+            // EXTEND a String test
+            var myStr = wf.declareStr("my-str");
+            wf.doIf(myStr.isNotEqualTo(null), then -> {
+                myStr.assignTo(myStr.extend("-suffix"));
+            });
+
+            // Add an int and composite expressions
+            var intToAdd = wf.declareInt("int-to-add");
+            var intToAddResult = wf.declareInt("int-to-add-result");
+            wf.doIf(intToAdd.isNotEqualTo(null), then -> {
+                // Tests compound expressions
+                intToAddResult.assignTo(wf.execute("expr-add-one", intToAdd.add(1)));
+            });
+
+            // Division By Zero test
+            var thingToDivideByZero = wf.declareInt("thing-to-divide-by-zero");
+            var divideByZeroResult = wf.declareInt("divide-by-zero-result");
+            wf.doIf(thingToDivideByZero.isNotEqualTo(null), then -> {
+                divideByZeroResult.assignTo(thingToDivideByZero.divide(0));
+            });
+
+            // Test precision of arithmetic. Make use of the fact that we don't have
+            // strong typing on json objects so that we can use a jsonpath to arbitrarily
+            // set input values.
+            var divisionTestJson = wf.declareJsonObj("dividend-tests");
+            var divisionResult = wf.declareDouble("division-result");
+            var divisionResultInt = wf.declareInt("division-result-int");
+            wf.doIf(divisionTestJson.isNotEqualTo(null), then -> {
+                LHExpression foobar = divisionTestJson.jsonPath("$.lhs").divide(divisionTestJson.jsonPath("$.rhs"));
+                divisionResult.assignTo(foobar);
+                divisionResultInt.assignTo(foobar);
+            });
+
+            // This test uses a complex expression where the things we are computing over
+            // have the double precision. We want to make sure that the computation is executed
+            // with double precision whether we assign the result to an int or a double.
+            var quantity = wf.declareInt("quantity");
+            var price = wf.declareDouble("price");
+            var discountPercentage = wf.declareInt("discount-percentage");
+            var totalPriceInt = wf.declareInt("total-price-int");
+            var totalPriceDouble = wf.declareDouble("total-price-double");
+            wf.doIf(quantity.isNotEqualTo(null), then -> {
+                // TotalPrice = Quantity * Price * (1 - DiscountPercentage / 100)
+                LHExpression pedro =
+                        quantity.multiply(price).multiply(wf.subtract(1.0, discountPercentage.divide(100.0)));
+                totalPriceInt.assignTo(pedro);
+                totalPriceDouble.assignTo(pedro);
+            });
+
+            // Test mutating sub-fields of a json object
+            var json = wf.declareJsonObj("json");
+            wf.doIf(json.isNotEqualTo(null), then -> {
+                json.jsonPath("$.foo").assignTo("bar");
+            });
+
+            // Test mutating doubly-nested fields of a Json Object
+            var nestedJson = wf.declareJsonObj("nested-json");
+            wf.doIf(nestedJson.isNotEqualTo(null), then -> {
+                nestedJson.jsonPath("$.foo.bar").assignTo("baz");
+            });
+        });
+    }
+
+    @LHTaskMethod("expr-add-one")
+    public int addOne(int input) {
+        return input + 1;
+    }
+}
diff --git a/server/src/test/java/e2e/VarSubErrorTest.java b/server/src/test/java/e2e/VarSubErrorTest.java
index 62f2cf568..cefe983c1 100644
--- a/server/src/test/java/e2e/VarSubErrorTest.java
+++ b/server/src/test/java/e2e/VarSubErrorTest.java
@@ -109,19 +109,6 @@ void shouldFindVarSubErrorOnFirstNodeRun() {
                 .start();
     }
 
-    @Test
-    void shouldThrowVarSubErrorWhenKeyMissingFromJsonObj() {
-        verifier.prepareRun(varTypeValidationsWf, Arg.of("input-int", 123), Arg.of("input-json", Map.of("str", "yoda")))
-                .waitForStatus(LHStatus.ERROR)
-                .thenVerifyNodeRun(0, 1, nodeRun -> {
-                    assertThat(nodeRun.getFailuresCount()).isEqualTo(1);
-                    Failure failure = nodeRun.getFailures(0);
-                    assertThat(failure.getFailureName()).isEqualTo(LHErrorType.VAR_SUB_ERROR.toString());
-                    assertThat(failure.getMessage()).contains("$.int");
-                })
-                .start();
-    }
-
     @Test
     void shouldBeAbleToPassNullAsIntIntoTaskRunAndTaskRunShouldFail() {
         Map<String, String> jsonStuff = new HashMap<>();
diff --git a/server/src/test/java/e2e/VariablesTest.java b/server/src/test/java/e2e/VariablesTest.java
index 75d77afce..cf1a80324 100644
--- a/server/src/test/java/e2e/VariablesTest.java
+++ b/server/src/test/java/e2e/VariablesTest.java
@@ -65,7 +65,7 @@ public void shouldMaskVariableValues() {
 
     @Test
     public void shouldHandleVarSubErrors() {
-        final String expectedMessage = "Caught unexpected error when mutating variables: / by zero";
+        final String expectedMessage = "Cannot divide by zero";
         workflowVerifier
                 .prepareRun(mutationWf, Arg.of("value-a", 9), Arg.of("value-b", 0))
                 .waitForStatus(LHStatus.ERROR)
diff --git a/server/src/test/java/io/littlehorse/server/auth/RequestSanitizerTest.java b/server/src/test/java/io/littlehorse/server/auth/InsecureAuthenticatorTest.java
similarity index 66%
rename from server/src/test/java/io/littlehorse/server/auth/RequestSanitizerTest.java
rename to server/src/test/java/io/littlehorse/server/auth/InsecureAuthenticatorTest.java
index a830ac0b5..3c021628a 100644
--- a/server/src/test/java/io/littlehorse/server/auth/RequestSanitizerTest.java
+++ b/server/src/test/java/io/littlehorse/server/auth/InsecureAuthenticatorTest.java
@@ -12,15 +12,17 @@
 import io.grpc.ServerInterceptors;
 import io.grpc.ServerMethodDefinition;
 import io.grpc.ServerServiceDefinition;
+import io.littlehorse.common.LHConstants;
 import io.littlehorse.sdk.common.proto.LittleHorseGrpc;
+import io.littlehorse.server.auth.authenticators.InsecureAuthenticator;
 import java.util.Collection;
 import lombok.Getter;
 import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.Test;
 
-class RequestSanitizerTest {
+class InsecureAuthenticatorTest {
 
-    private RequestSanitizer sanitizer = new RequestSanitizer();
+    private InsecureAuthenticator authenticator = new InsecureAuthenticator();
     private TrackableInterceptor trackableInterceptor = new TrackableInterceptor();
     private final ServerServiceDefinition testServiceDefinition = buildTestServiceDefinition(
             ServerServiceDefinition.builder(LittleHorseGrpc.getServiceDescriptor()),
@@ -30,19 +32,30 @@ class RequestSanitizerTest {
     private final Metadata requestHeaders = new Metadata();
 
     @Test
-    public void shouldRemoveInternalHeader() {
-        requestHeaders.put(ServerAuthorizer.CLIENT_ID, "root");
-        requestHeaders.put(ServerAuthorizer.TENANT_ID, "my-tenant");
+    public void shouldSetPrincipalToAnonymousWhenProvidedByUser() {
+        requestHeaders.put(LHServerInterceptor.CLIENT_ID, "root");
+        requestHeaders.put(LHServerInterceptor.TENANT_ID, "my-tenant");
         startCall();
         Metadata resolvedHeaders = trackableInterceptor.getHeaders();
         Assertions.assertThat(resolvedHeaders).isNotNull();
-        Assertions.assertThat(resolvedHeaders.get(ServerAuthorizer.CLIENT_ID)).isNull();
-        Assertions.assertThat(resolvedHeaders.get(ServerAuthorizer.TENANT_ID)).isEqualTo("my-tenant");
+        Assertions.assertThat(resolvedHeaders.get(LHServerInterceptor.CLIENT_ID))
+                .isEqualTo(LHConstants.ANONYMOUS_PRINCIPAL);
+        Assertions.assertThat(resolvedHeaders.get(LHServerInterceptor.TENANT_ID))
+                .isEqualTo("my-tenant");
+    }
+
+    @Test
+    public void shouldSetPrincipalToAnonymous() {
+        startCall();
+        Metadata resolvedHeaders = trackableInterceptor.getHeaders();
+        Assertions.assertThat(resolvedHeaders).isNotNull();
+        Assertions.assertThat(resolvedHeaders.get(LHServerInterceptor.CLIENT_ID))
+                .isEqualTo(LHConstants.ANONYMOUS_PRINCIPAL);
     }
 
     private void startCall() {
         ServerServiceDefinition intercept =
-                ServerInterceptors.intercept(testServiceDefinition, sanitizer, trackableInterceptor);
+                ServerInterceptors.intercept(testServiceDefinition, authenticator, trackableInterceptor);
         @SuppressWarnings("unchecked")
         ServerMethodDefinition<Object, Object> def =
                 (ServerMethodDefinition<Object, Object>) Iterables.get(intercept.getMethods(), 0);
@@ -58,7 +71,7 @@ private ServerServiceDefinition buildTestServiceDefinition(
     }
 
     @Getter
-    private static class TrackableInterceptor implements ServerAuthorizer {
+    private static class TrackableInterceptor implements LHServerInterceptor {
         private Metadata headers;
 
         @Override
diff --git a/server/src/test/java/io/littlehorse/server/auth/RequestAuthorizerTest.java b/server/src/test/java/io/littlehorse/server/auth/RequestAuthorizerTest.java
index 5676fc808..74d7efd04 100644
--- a/server/src/test/java/io/littlehorse/server/auth/RequestAuthorizerTest.java
+++ b/server/src/test/java/io/littlehorse/server/auth/RequestAuthorizerTest.java
@@ -89,7 +89,7 @@ private void startCall() {
 
     @Test
     public void supportAnonymousPrincipalForDefaultTenant() {
-        when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn(null);
+        when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn(null);
 
         startCall();
         assertThat(resolvedAuthContext).isNotNull();
@@ -102,7 +102,7 @@ public void supportAnonymousPrincipalForDefaultTenant() {
 
     @Test
     public void supportAnonymousPrincipalWhenClientIdIsNotFound() {
-        when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("principal-id");
+        when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("principal-id");
         startCall();
         assertThat(resolvedAuthContext.principalId().getId()).isEqualTo(LHConstants.ANONYMOUS_PRINCIPAL);
         assertThat(resolvedAuthContext.acls())
@@ -111,8 +111,8 @@ public void supportAnonymousPrincipalWhenClientIdIsNotFound() {
 
     @Test
     public void supportPrincipalForSpecificTenant() {
-        when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("principal-id");
-        when(mockMetadata.get(ServerAuthorizer.TENANT_ID)).thenReturn("my-tenant");
+        when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("principal-id");
+        when(mockMetadata.get(LHServerInterceptor.TENANT_ID)).thenReturn("my-tenant");
         PrincipalModel newPrincipal = new PrincipalModel();
         newPrincipal.setId(new PrincipalIdModel("principal-id"));
         newPrincipal.setGlobalAcls(TestUtil.singleAdminAcl("name"));
@@ -126,8 +126,8 @@ public void supportPrincipalForSpecificTenant() {
 
     @Test
     public void supportPermissionDeniedForNonExistingTenants() {
-        when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("principal-id");
-        when(mockMetadata.get(ServerAuthorizer.TENANT_ID)).thenReturn("my-missing-tenant");
+        when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("principal-id");
+        when(mockMetadata.get(LHServerInterceptor.TENANT_ID)).thenReturn("my-missing-tenant");
         PrincipalModel newPrincipal = new PrincipalModel();
         newPrincipal.setId(new PrincipalIdModel("principal-id"));
         newPrincipal.setGlobalAcls(TestUtil.singleAdminAcl("name"));
@@ -138,7 +138,7 @@ public void supportPermissionDeniedForNonExistingTenants() {
 
     @Test
     public void supportAnonymousPrincipalWhenPrincipalIdIsNotFound() {
-        when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("principal-id");
+        when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("principal-id");
         metadataManager.put(new TenantModel("my-tenant"));
         startCall();
         assertThat(resolvedAuthContext.principalId().getId()).isEqualTo(LHConstants.ANONYMOUS_PRINCIPAL);
@@ -164,7 +164,7 @@ public void setup() {
 
         @Test
         public void supportRequestAuthorizationForAdminPrincipals() {
-            when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("admin-principal");
+            when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("admin-principal");
             startCall();
             assertThat(resolvedAuthContext).isNotNull();
         }
@@ -174,7 +174,7 @@ public void supportRequiredAclValidation() {
             MethodDescriptor<Object, Object> mockMethod = mock();
             when(mockCall.getMethodDescriptor()).thenReturn(mockMethod);
             when(mockMethod.getBareMethodName()).thenReturn("PutTaskDef");
-            when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("limited-principal");
+            when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("limited-principal");
             startCall();
             Mockito.verify(mockCall).close(any(), eq(mockMetadata));
         }
@@ -184,7 +184,7 @@ public void shouldRejectTenantResourceRequestFromTenantAdminPrincipal() {
             MethodDescriptor<Object, Object> mockMethod = mock();
             when(mockCall.getMethodDescriptor()).thenReturn(mockMethod);
             when(mockMethod.getBareMethodName()).thenReturn("PutTenant");
-            when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("tenant-admin-principal");
+            when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("tenant-admin-principal");
             startCall();
             ArgumentCaptor<Status> statusCaptor = ArgumentCaptor.forClass(Status.class);
             Mockito.verify(mockCall).close(statusCaptor.capture(), eq(mockMetadata));
@@ -199,7 +199,7 @@ public void shouldRejectPrincipalResourceRequestFromTenantAdminPrincipal() {
             MethodDescriptor<Object, Object> mockMethod = mock();
             when(mockCall.getMethodDescriptor()).thenReturn(mockMethod);
             when(mockMethod.getBareMethodName()).thenReturn("PutPrincipal");
-            when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("tenant-admin-principal");
+            when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("tenant-admin-principal");
             startCall();
             ArgumentCaptor<Status> statusCaptor = ArgumentCaptor.forClass(Status.class);
             Mockito.verify(mockCall).close(statusCaptor.capture(), eq(mockMetadata));
@@ -214,8 +214,8 @@ public void supportTenantAdmins() {
             MethodDescriptor<Object, Object> mockMethod = mock();
             when(mockCall.getMethodDescriptor()).thenReturn(mockMethod);
             when(mockMethod.getBareMethodName()).thenReturn("PutTaskDef");
-            when(mockMetadata.get(ServerAuthorizer.CLIENT_ID)).thenReturn("tenant-admin-principal");
-            when(mockMetadata.get(ServerAuthorizer.TENANT_ID)).thenReturn("my-tenant");
+            when(mockMetadata.get(LHServerInterceptor.CLIENT_ID)).thenReturn("tenant-admin-principal");
+            when(mockMetadata.get(LHServerInterceptor.TENANT_ID)).thenReturn("my-tenant");
             startCall();
             assertThat(resolvedAuthContext).isNotNull();
         }
@@ -261,7 +261,7 @@ public MethodDescriptor<Object, Object> getMethodDescriptor() {
                 }
             };
             final Metadata mockMetadata = new Metadata();
-            mockMetadata.put(ServerAuthorizer.CLIENT_ID, principalId);
+            mockMetadata.put(LHServerInterceptor.CLIENT_ID, principalId);
             PrincipalModel newPrincipal = new PrincipalModel();
             newPrincipal.setId(new PrincipalIdModel(principalId));
             newPrincipal.setGlobalAcls(TestUtil.singleAdminAcl("name"));
@@ -313,7 +313,7 @@ private ServerServiceDefinition buildContextPropagationVerifierServiceDefinition
             definitionBuilder = definitionBuilder.addMethod(method, (call, headers) -> {
                 String principalId =
                         contextKey.get().authorization().principalId().toString();
-                assertThat(principalId).isEqualTo(headers.get(ServerAuthorizer.CLIENT_ID));
+                assertThat(principalId).isEqualTo(headers.get(LHServerInterceptor.CLIENT_ID));
                 return new NoopServerCall.NoopServerCallListener<>();
             });
         }
diff --git a/test-utils/src/main/java/io/littlehorse/test/WfRunVerifier.java b/test-utils/src/main/java/io/littlehorse/test/WfRunVerifier.java
index dd195c603..83a3227b5 100644
--- a/test-utils/src/main/java/io/littlehorse/test/WfRunVerifier.java
+++ b/test-utils/src/main/java/io/littlehorse/test/WfRunVerifier.java
@@ -27,6 +27,7 @@
 import io.littlehorse.test.internal.step.SearchStep;
 import io.littlehorse.test.internal.step.SendExternalEventStep;
 import io.littlehorse.test.internal.step.VerifyAllTaskRunsStep;
+import io.littlehorse.test.internal.step.VerifyLastNodeRunStep;
 import io.littlehorse.test.internal.step.VerifyNodeRunStep;
 import io.littlehorse.test.internal.step.VerifyTaskExecution;
 import io.littlehorse.test.internal.step.VerifyTaskRunOutputsStep;
@@ -174,6 +175,11 @@ public WfRunVerifier thenVerifyNodeRun(int threadRunNumber, int nodeRunNumber, C
         return this;
     }
 
+    public WfRunVerifier thenVerifyLastNodeRun(int threadRunNumber, Consumer<NodeRun> matcher) {
+        steps.add(new VerifyLastNodeRunStep(threadRunNumber, matcher, steps.size() + 1));
+        return this;
+    }
+
     public WfRunVerifier waitForTaskStatus(int threadRunNumber, int nodeRunNumber, TaskStatus taskStatus) {
         Function<TestExecutionContext, TaskStatus> objectLHStatusFunction = context -> {
             NodeRun nodeRun = lhClient.getNodeRun(nodeRunIdFrom(context.getWfRunId(), threadRunNumber, nodeRunNumber));
diff --git a/test-utils/src/main/java/io/littlehorse/test/internal/TestBootstrapper.java b/test-utils/src/main/java/io/littlehorse/test/internal/TestBootstrapper.java
index f89c0a967..6416ca5dd 100644
--- a/test-utils/src/main/java/io/littlehorse/test/internal/TestBootstrapper.java
+++ b/test-utils/src/main/java/io/littlehorse/test/internal/TestBootstrapper.java
@@ -6,7 +6,7 @@
 import io.littlehorse.common.model.getable.objectId.TenantIdModel;
 import io.littlehorse.sdk.common.config.LHConfig;
 import io.littlehorse.sdk.common.proto.LittleHorseGrpc.LittleHorseBlockingStub;
-import io.littlehorse.server.auth.ServerAuthorizer;
+import io.littlehorse.server.auth.LHServerInterceptor;
 import java.util.concurrent.Executor;
 
 public interface TestBootstrapper {
@@ -28,7 +28,7 @@ public void applyRequestMetadata(RequestInfo requestInfo, Executor executor, Met
                 try {
                     Metadata headers = new Metadata();
                     if (tenantId != null && tenantId.getId() != null) {
-                        headers.put(ServerAuthorizer.TENANT_ID, tenantId.getId());
+                        headers.put(LHServerInterceptor.TENANT_ID, tenantId.getId());
                         metadataApplier.apply(headers);
                     }
                 } catch (Exception e) {
diff --git a/test-utils/src/main/java/io/littlehorse/test/internal/step/VerifyLastNodeRunStep.java b/test-utils/src/main/java/io/littlehorse/test/internal/step/VerifyLastNodeRunStep.java
new file mode 100644
index 000000000..94ffe5d82
--- /dev/null
+++ b/test-utils/src/main/java/io/littlehorse/test/internal/step/VerifyLastNodeRunStep.java
@@ -0,0 +1,33 @@
+package io.littlehorse.test.internal.step;
+
+import io.littlehorse.sdk.common.proto.LittleHorseGrpc.LittleHorseBlockingStub;
+import io.littlehorse.sdk.common.proto.NodeRun;
+import io.littlehorse.sdk.common.proto.NodeRunId;
+import io.littlehorse.test.internal.TestExecutionContext;
+import java.util.function.Consumer;
+
+public class VerifyLastNodeRunStep extends AbstractStep {
+
+    private final int threadRunNumber;
+    private final Consumer<NodeRun> matcher;
+
+    public VerifyLastNodeRunStep(int threadRunNumber, Consumer<NodeRun> matcher, int id) {
+        super(id);
+        this.threadRunNumber = threadRunNumber;
+        this.matcher = matcher;
+    }
+
+    @Override
+    public void tryExecute(TestExecutionContext context, LittleHorseBlockingStub lhClient) {
+        int nodePosition = lhClient.getWfRun(context.getWfRunId())
+                .getThreadRuns(threadRunNumber)
+                .getCurrentNodePosition();
+        NodeRunId id = NodeRunId.newBuilder()
+                .setWfRunId(context.getWfRunId())
+                .setThreadRunNumber(threadRunNumber)
+                .setPosition(nodePosition)
+                .build();
+        NodeRun nodeRun = lhClient.getNodeRun(id);
+        matcher.accept(nodeRun);
+    }
+}