diff --git a/contracts/validator-manager/ACP99Manager.sol b/contracts/validator-manager/ACP99Manager.sol
new file mode 100644
index 000000000..80b5e2d74
--- /dev/null
+++ b/contracts/validator-manager/ACP99Manager.sol
@@ -0,0 +1,212 @@
+// (c) 2025, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+// SPDX-License-Identifier: Ecosystem
+
+pragma solidity 0.8.25;
+
+/**
+ * @notice Description of the conversion data used to convert
+ * a subnet to an L1 on the P-Chain.
+ * This data is the pre-image of a hash that is authenticated by the P-Chain
+ * and verified by the Validator Manager.
+ */
+struct ConversionData {
+    bytes32 subnetID;
+    bytes32 validatorManagerBlockchainID;
+    address validatorManagerAddress;
+    InitialValidator[] initialValidators;
+}
+
+/// @notice Specifies an initial validator, used in the conversion data.
+struct InitialValidator {
+    bytes nodeID;
+    bytes blsPublicKey;
+    uint64 weight;
+}
+
+/// @notice L1 validator status
+enum ValidatorStatus {
+    Unknown,
+    PendingAdded,
+    Active,
+    PendingRemoved,
+    Completed,
+    Invalidated
+}
+
+/**
+ * @notice Specifies the owner of a validator's remaining balance or disable owner on the P-Chain.
+ * P-Chain addresses are also 20-bytes, so we use the address type to represent them.
+ */
+struct PChainOwner {
+    uint32 threshold;
+    address[] addresses;
+}
+
+/**
+ * @notice Contains the active state of a Validator
+ * @param status The validator status
+ * @param nodeID The NodeID of the validator
+ * @param startingWeight The weight of the validator at the time of registration
+ * @param messageNonce The current weight update nonce
+ * @param weight The current weight of the validator
+ * @param startTime The start time of the validator
+ * @param endTime The end time of the validator
+ */
+struct Validator {
+    ValidatorStatus status;
+    bytes nodeID;
+    uint64 startingWeight;
+    uint64 sentNonce;
+    uint64 receivedNonce;
+    uint64 weightChangedAt;
+    uint64 weight;
+    uint64 startTime;
+    uint64 endTime;
+}
+
+/*
+ * @title ACP99Manager
+ * @notice The ACP99Manager interface represents the functionality for sovereign L1
+ * validator management, as specified in ACP-77
+ */
+abstract contract ACP99Manager {
+    /// @notice Emitted when an initial validator is registered
+    event RegisteredInitialValidator(
+        bytes32 indexed nodeID, bytes32 indexed validationID, uint64 weight
+    );
+    /// @notice Emitted when a validator registration to the L1 is initiated
+    event InitiatedValidatorRegistration(
+        bytes32 indexed nodeID,
+        bytes32 indexed validationID,
+        bytes32 registrationMessageID,
+        uint64 registrationExpiry,
+        uint64 weight
+    );
+    /// @notice Emitted when a validator registration to the L1 is completed
+    event CompletedValidatorRegistration(
+        bytes32 indexed nodeID, bytes32 indexed validationID, uint64 weight
+    );
+    /// @notice Emitted when a validator weight update is initiated
+    event InitiatedValidatorWeightUpdate(
+        bytes32 indexed nodeID,
+        bytes32 indexed validationID,
+        bytes32 weightUpdateMessageID,
+        uint64 weight
+    );
+    /// @notice Emitted when a validator weight update is completed
+    event CompletedValidatorWeightUpdate(
+        bytes32 indexed nodeID, bytes32 indexed validationID, uint64 nonce, uint64 weight
+    );
+
+    /**
+     * @notice Verifies and sets the initial validator set for the chain through a P-Chain
+     * SubnetToL1ConversionMessage.
+     * 
+     * Emits a {RegisteredInitialValidator} event for each initial validator in {conversionData}.
+     *
+     * @param conversionData The Subnet conversion message data used to recompute and verify against the ConversionID.
+     * @param messsageIndex The index that contains the SubnetToL1ConversionMessage Warp message containing the ConversionID to be verified against the provided {conversionData}
+     */
+    function initializeValidatorSet(
+        ConversionData calldata conversionData,
+        uint32 messsageIndex
+    ) virtual public;
+
+    /**
+     * @notice Completes the validator registration process by returning an acknowledgement of the registration of a
+     * validationID from the P-Chain. The validator should not be considered active until this method is successfully called.
+     *
+     * Emits a {CompletedValidatorRegistration} event on success.
+     *
+     * @param messageIndex The index of the Warp message to be received providing the acknowledgement.
+     */
+    function completeValidatorRegistration(
+        uint32 messageIndex
+    ) virtual public returns (bytes32);
+
+    /**
+    * @notice Initiates validator removal by issuing a L1ValidatorWeightMessage with the weight set to zero.
+    * The validator should be considered inactive as soon as this function is called.
+    *
+    * Emits an {InitiatedValidatorRemoval} on success.
+    *
+    * @param validationID The ID of the validator to remove.
+    */
+    function _initiateValidatorRemoval(
+        bytes32 validationID
+    ) virtual internal;
+
+    /**
+    * @notice Completes validator removal by consuming an RegisterL1ValidatorMessage from the P-Chain acknowledging
+    * that the validator has been removed.
+    *
+    * Emits a {CompletedValidatorRemoval} on success.
+    *
+    * @param messageIndex The index of the RegisterL1ValidatorMessage.
+    */
+    function completeValidatorRemoval(
+        uint32 messageIndex
+    ) virtual public returns (bytes32 validationID);
+
+    /**
+     * @notice Completes the validator weight update process by returning an acknowledgement of the weight update of a
+     * validationID from the P-Chain. The validator weight change should not have any effect until this method is successfully called.
+     *
+     * Emits a {CompletedValidatorWeightUpdate} event on success
+     *
+     * @param messageIndex The index of the Warp message to be received providing the acknowledgement.
+     */
+    function completeValidatorWeightUpdate(
+        uint32 messageIndex
+    ) virtual public returns (bytes32);
+
+    /// @notice Returns the ID of the Subnet tied to this manager
+    function subnetID() virtual public view returns (bytes32);
+
+    /// @notice Returns the validation details for a given validation ID
+    function getValidator(
+        bytes32 validationID
+    ) virtual public view returns (Validator memory);
+
+    /// @notice Returns the total weight of the current L1 validator set
+    function l1TotalWeight() virtual public view returns (uint64);
+
+    /**
+     * @notice Initiate a validator registration by issuing a RegisterL1ValidatorTx Warp message. The validator should
+     * not be considered active until completeValidatorRegistration is called.
+     *
+     * Emits an {InitiatedValidatorRegistration} event on success.
+     *
+     * @param nodeID The ID of the node to add to the L1
+     * @param blsPublicKey The BLS public key of the validator
+     * @param registrationExpiry The time after which this message is invalid
+     * @param remainingBalanceOwner The remaining balance owner of the validator
+     * @param disableOwner The disable owner of the validator
+     * @param weight The weight of the node on the L1
+     */
+    function _initiateValidatorRegistration(
+        bytes memory nodeID,
+        bytes memory blsPublicKey,
+        uint64 registrationExpiry,
+        PChainOwner memory remainingBalanceOwner,
+        PChainOwner memory disableOwner,
+        uint64 weight
+    ) virtual internal returns (bytes32);
+
+    /**
+     * @notice Initiate a validator weight update by issuing a SetL1ValidatorWeightTx Warp message.
+     * If the weight is 0, this initiates the removal of the validator from the L1. The validator weight change
+     * should not have any effect until completeValidatorWeightUpdate is successfully called.
+     *
+     * Emits an {InitiatedValidatorWeightUpdate} event on success.
+     *
+     * @param validationID The ID of the validation period to modify
+     * @param weight The new weight of the validation
+     */
+    function _initiateValidatorWeightUpdate(
+        bytes32 validationID,
+        uint64 weight
+    ) virtual internal returns (uint64, bytes32);
+}
\ No newline at end of file
diff --git a/contracts/validator-manager/ExampleRewardCalculator.sol b/contracts/validator-manager/ExampleRewardCalculator.sol
index 856158350..7ef351e62 100644
--- a/contracts/validator-manager/ExampleRewardCalculator.sol
+++ b/contracts/validator-manager/ExampleRewardCalculator.sol
@@ -31,7 +31,7 @@ contract ExampleRewardCalculator is IRewardCalculator {
         uint64 stakingEndTime,
         uint64 uptimeSeconds
     ) external view returns (uint256) {
-        // Equivalent to uptimeSeconds/(validator.endedAt - validator.startedAt) < UPTIME_REWARDS_THRESHOLD_PERCENTAGE/100
+        // Equivalent to uptimeSeconds/(validator.endTime - validator.startTime) < UPTIME_REWARDS_THRESHOLD_PERCENTAGE/100
         // Rearranged to prevent integer division truncation.
         if (
             uptimeSeconds * 100
diff --git a/contracts/validator-manager/PoAValidatorManager.sol b/contracts/validator-manager/PoAValidatorManager.sol
index b62a30557..6544f64fd 100644
--- a/contracts/validator-manager/PoAValidatorManager.sol
+++ b/contracts/validator-manager/PoAValidatorManager.sol
@@ -55,7 +55,14 @@ contract PoAValidatorManager is IPoAValidatorManager, ValidatorManager, OwnableU
         ValidatorRegistrationInput calldata registrationInput,
         uint64 weight
     ) external onlyOwner returns (bytes32 validationID) {
-        return _initializeValidatorRegistration(registrationInput, weight);
+        return _initiateValidatorRegistration({
+            nodeID: registrationInput.nodeID,
+            blsPublicKey: registrationInput.blsPublicKey,
+            registrationExpiry: registrationInput.registrationExpiry,
+            remainingBalanceOwner: registrationInput.remainingBalanceOwner,
+            disableOwner: registrationInput.disableOwner,
+            weight: weight
+        });
     }
 
     // solhint-enable ordering
@@ -63,13 +70,14 @@ contract PoAValidatorManager is IPoAValidatorManager, ValidatorManager, OwnableU
      * @notice See {IPoAValidatorManager-initializeEndValidation}.
      */
     function initializeEndValidation(bytes32 validationID) external override onlyOwner {
-        _initializeEndValidation(validationID);
+        _initiateValidatorRemoval(validationID);
     }
 
     /**
      * @notice See {IValidatorManager-completeEndValidation}.
      */
-    function completeEndValidation(uint32 messageIndex) external {
-        _completeEndValidation(messageIndex);
+    function completeValidatorRemoval(uint32 messageIndex) virtual override public returns (bytes32) {
+        (bytes32 validationID,) =  _completeEndValidation(messageIndex);
+        return validationID;
     }
 }
diff --git a/contracts/validator-manager/PoSValidatorManager.sol b/contracts/validator-manager/PoSValidatorManager.sol
index 22ebc6120..0a1e2f5b5 100644
--- a/contracts/validator-manager/PoSValidatorManager.sol
+++ b/contracts/validator-manager/PoSValidatorManager.sol
@@ -14,11 +14,13 @@ import {
     PoSValidatorInfo,
     PoSValidatorManagerSettings
 } from "./interfaces/IPoSValidatorManager.sol";
+import {
+    ValidatorRegistrationInput
+} from "./interfaces/IValidatorManager.sol";
 import {
     Validator,
-    ValidatorRegistrationInput,
     ValidatorStatus
-} from "./interfaces/IValidatorManager.sol";
+} from "./ACP99Manager.sol";
 import {IRewardCalculator} from "./interfaces/IRewardCalculator.sol";
 import {WarpMessage} from
     "@avalabs/subnet-evm-contracts@1.2.0/contracts/interfaces/IWarpMessenger.sol";
@@ -85,7 +87,6 @@ abstract contract PoSValidatorManager is
     error InvalidDelegationFee(uint16 delegationFeeBips);
     error InvalidDelegationID(bytes32 delegationID);
     error InvalidDelegatorStatus(DelegatorStatus status);
-    error InvalidNonce(uint64 nonce);
     error InvalidRewardRecipient(address rewardRecipient);
     error InvalidStakeAmount(uint256 stakeAmount);
     error InvalidMinStakeDuration(uint64 minStakeDuration);
@@ -327,7 +328,8 @@ abstract contract PoSValidatorManager is
     ) internal returns (bool) {
         PoSValidatorManagerStorage storage $ = _getPoSValidatorManagerStorage();
 
-        Validator memory validator = _initializeEndValidation(validationID);
+        Validator memory validator = getValidator(validationID);
+        _initiateValidatorRemoval(validationID);
 
         // Non-PoS validators are required to boostrap the network, but are not eligible for rewards.
         if (!_isPoSValidator(validationID)) {
@@ -341,10 +343,10 @@ abstract contract PoSValidatorManager is
 
         // Check that minimum stake duration has passed.
         if (
-            validator.endedAt
-                < validator.startedAt + $._posValidatorInfo[validationID].minStakeDuration
+            validator.endTime
+                < validator.startTime + $._posValidatorInfo[validationID].minStakeDuration
         ) {
-            revert MinStakeDurationNotPassed(validator.endedAt);
+            revert MinStakeDurationNotPassed(validator.endTime);
         }
 
         // Uptime proofs include the absolute number of seconds the validator has been active.
@@ -357,9 +359,9 @@ abstract contract PoSValidatorManager is
 
         uint256 reward = $._rewardCalculator.calculateReward({
             stakeAmount: weightToValue(validator.startingWeight),
-            validatorStartTime: validator.startedAt,
-            stakingStartTime: validator.startedAt,
-            stakingEndTime: validator.endedAt,
+            validatorStartTime: validator.startTime,
+            stakingStartTime: validator.startTime,
+            stakingEndTime: validator.endTime,
             uptimeSeconds: uptimeSeconds
         });
 
@@ -374,9 +376,9 @@ abstract contract PoSValidatorManager is
     }
 
     /**
-     * @notice See {IValidatorManager-completeEndValidation}.
+     * @notice See {ACP99Manager-completeValidatorRemoval}.
      */
-    function completeEndValidation(uint32 messageIndex) external nonReentrant {
+    function completeValidatorRemoval(uint32 messageIndex) virtual override public nonReentrant returns (bytes32) {
         PoSValidatorManagerStorage storage $ = _getPoSValidatorManagerStorage();
 
         (bytes32 validationID, Validator memory validator) = _completeEndValidation(messageIndex);
@@ -384,7 +386,7 @@ abstract contract PoSValidatorManager is
         // Return now if this was originally a PoA validator that was later migrated to this PoS manager,
         // or the validator was part of the initial validator set.
         if (!_isPoSValidator(validationID)) {
-            return;
+            return validationID;
         }
 
         address owner = $._posValidatorInfo[validationID].owner;
@@ -403,6 +405,8 @@ abstract contract PoSValidatorManager is
 
         // The stake is unlocked whether the validation period is completed or invalidated.
         _unlock(owner, weightToValue(validator.startingWeight));
+
+        return validationID;
     }
 
     /**
@@ -475,7 +479,14 @@ abstract contract PoSValidatorManager is
         uint256 lockedValue = _lock(stakeAmount);
 
         uint64 weight = valueToWeight(lockedValue);
-        bytes32 validationID = _initializeValidatorRegistration(registrationInput, weight);
+        bytes32 validationID = _initiateValidatorRegistration({
+            nodeID: registrationInput.nodeID,
+            blsPublicKey: registrationInput.blsPublicKey,
+            registrationExpiry: registrationInput.registrationExpiry,
+            remainingBalanceOwner: registrationInput.remainingBalanceOwner,
+            disableOwner: registrationInput.disableOwner,
+            weight: weight
+        });
 
         address owner = _msgSender();
 
@@ -545,7 +556,7 @@ abstract contract PoSValidatorManager is
             revert MaxWeightExceeded(newValidatorWeight);
         }
 
-        (uint64 nonce, bytes32 messageID) = _setValidatorWeight(validationID, newValidatorWeight);
+        (uint64 nonce, bytes32 messageID) = _initiateValidatorWeightUpdate(validationID, newValidatorWeight);
 
         bytes32 delegationID = keccak256(abi.encodePacked(validationID, nonce));
 
@@ -556,7 +567,7 @@ abstract contract PoSValidatorManager is
         $._delegatorStakes[delegationID].owner = delegatorAddress;
         $._delegatorStakes[delegationID].validationID = validationID;
         $._delegatorStakes[delegationID].weight = weight;
-        $._delegatorStakes[delegationID].startedAt = 0;
+        $._delegatorStakes[delegationID].startTime = 0;
         $._delegatorStakes[delegationID].startingNonce = nonce;
         $._delegatorStakes[delegationID].endingNonce = 0;
 
@@ -595,25 +606,22 @@ abstract contract PoSValidatorManager is
             return _completeEndDelegation(delegationID);
         }
 
-        // Unpack the Warp message
-        (bytes32 messageValidationID, uint64 nonce,) = ValidatorMessages
-            .unpackL1ValidatorWeightMessage(_getPChainWarpMessage(messageIndex).payload);
-
-        if (validationID != messageValidationID) {
-            revert InvalidValidationID(delegator.validationID);
+        // If we've already received a weight update with a nonce greater than the delegation's starting nonce,
+        // then there's no requirement to include an ICM message in this function call.
+        if (validator.receivedNonce < delegator.startingNonce) {
+            bytes32 messageValidationID = completeValidatorWeightUpdate(messageIndex);
+            if (validationID != messageValidationID) {
+                revert InvalidValidationID(delegator.validationID);
+            }
+            if (validator.receivedNonce < delegator.startingNonce) {
+                revert InvalidNonce(validator.receivedNonce);
+            }
         }
 
-        // The received nonce should be no greater than the highest sent nonce, and at least as high as
-        // the delegation's starting nonce. This allows a weight update using a higher nonce
-        // (which implicitly includes the delegation's weight update) to be used to complete delisting
-        // for an earlier delegation. This is necessary because the P-Chain is only willing to sign the latest weight update.
-        if (validator.messageNonce < nonce || delegator.startingNonce > nonce) {
-            revert InvalidNonce(nonce);
-        }
 
         // Update the delegation status
         $._delegatorStakes[delegationID].status = DelegatorStatus.Active;
-        $._delegatorStakes[delegationID].startedAt = uint64(block.timestamp);
+        $._delegatorStakes[delegationID].startTime = uint64(block.timestamp);
 
         emit DelegatorRegistered({
             delegationID: delegationID,
@@ -720,7 +728,7 @@ abstract contract PoSValidatorManager is
 
             if (
                 block.timestamp
-                    < validator.startedAt + $._posValidatorInfo[validationID].minStakeDuration
+                    < validator.startTime + $._posValidatorInfo[validationID].minStakeDuration
             ) {
                 revert MinStakeDurationNotPassed(uint64(block.timestamp));
             }
@@ -728,7 +736,7 @@ abstract contract PoSValidatorManager is
 
         if (validator.status == ValidatorStatus.Active) {
             // Check that minimum stake duration has passed.
-            if (block.timestamp < delegator.startedAt + $._minimumStakeDuration) {
+            if (block.timestamp < delegator.startTime + $._minimumStakeDuration) {
                 revert MinStakeDurationNotPassed(uint64(block.timestamp));
             }
 
@@ -743,7 +751,7 @@ abstract contract PoSValidatorManager is
             $._delegatorStakes[delegationID].status = DelegatorStatus.PendingRemoved;
 
             ($._delegatorStakes[delegationID].endingNonce,) =
-                _setValidatorWeight(validationID, validator.weight - delegator.weight);
+                _initiateValidatorWeightUpdate(validationID, validator.weight - delegator.weight);
 
             uint256 reward =
                 _calculateAndSetDelegationReward(delegator, rewardRecipient, delegationID);
@@ -780,7 +788,7 @@ abstract contract PoSValidatorManager is
             validator.status == ValidatorStatus.PendingRemoved
                 || validator.status == ValidatorStatus.Completed
         ) {
-            delegationEndTime = validator.endedAt;
+            delegationEndTime = validator.endTime;
         } else if (validator.status == ValidatorStatus.Active) {
             delegationEndTime = uint64(block.timestamp);
         } else {
@@ -789,14 +797,14 @@ abstract contract PoSValidatorManager is
         }
 
         // Only give rewards in the case that the delegation started before the validator exited.
-        if (delegationEndTime <= delegator.startedAt) {
+        if (delegationEndTime <= delegator.startTime) {
             return 0;
         }
 
         uint256 reward = $._rewardCalculator.calculateReward({
             stakeAmount: weightToValue(delegator.weight),
-            validatorStartTime: validator.startedAt,
-            stakingStartTime: delegator.startedAt,
+            validatorStartTime: validator.startTime,
+            stakingStartTime: delegator.startTime,
             stakingEndTime: delegationEndTime,
             uptimeSeconds: $._posValidatorInfo[delegator.validationID].uptimeSeconds
         });
@@ -827,7 +835,7 @@ abstract contract PoSValidatorManager is
         }
 
         Validator memory validator = getValidator(delegator.validationID);
-        if (validator.messageNonce == 0) {
+        if (validator.sentNonce == 0) {
             // Should be unreachable.
             revert InvalidDelegationID(delegationID);
         }
@@ -835,7 +843,7 @@ abstract contract PoSValidatorManager is
         // Submit the message to the Warp precompile.
         WARP_MESSENGER.sendWarpMessage(
             ValidatorMessages.packL1ValidatorWeightMessage(
-                delegator.validationID, validator.messageNonce, validator.weight
+                delegator.validationID, validator.sentNonce, validator.weight
             )
         );
     }
@@ -843,6 +851,9 @@ abstract contract PoSValidatorManager is
     /**
      * @notice See {IPoSValidatorManager-completeEndDelegation}.
      */
+     // TODONOW: Rather than ending on a delegation by delegation basis,
+     // Can we instead track the highest acknowledged nonce, delivered via completeValidatorWeightChange?
+     // We'd still have a delegation specific collectDelegationRewards or similar, but that would check against this nonce.
     function completeEndDelegation(
         bytes32 delegationID,
         uint32 messageIndex
@@ -856,23 +867,22 @@ abstract contract PoSValidatorManager is
         if (delegator.status != DelegatorStatus.PendingRemoved) {
             revert InvalidDelegatorStatus(delegator.status);
         }
+        Validator memory validator = getValidator(delegator.validationID);
 
-        if (getValidator(delegator.validationID).status != ValidatorStatus.Completed) {
-            // Unpack the Warp message
-            WarpMessage memory warpMessage = _getPChainWarpMessage(messageIndex);
-            (bytes32 validationID, uint64 nonce,) =
-                ValidatorMessages.unpackL1ValidatorWeightMessage(warpMessage.payload);
-
+        // We only expect an ICM message if we haven't received a weight update with a nonce greater than the delegation's ending nonce
+        if (getValidator(delegator.validationID).status != ValidatorStatus.Completed && validator.receivedNonce < delegator.endingNonce) {
+            bytes32 validationID = completeValidatorWeightUpdate(messageIndex);
             if (delegator.validationID != validationID) {
                 revert InvalidValidationID(validationID);
             }
 
+            
             // The received nonce should be at least as high as the delegation's ending nonce. This allows a weight
             // update using a higher nonce (which implicitly includes the delegation's weight update) to be used to
             // complete delisting for an earlier delegation. This is necessary because the P-Chain is only willing
             // to sign the latest weight update.
-            if (delegator.endingNonce > nonce) {
-                revert InvalidNonce(nonce);
+            if (delegator.endingNonce > validator.receivedNonce) {
+                revert InvalidNonce(validator.receivedNonce);
             }
         }
 
@@ -887,7 +897,8 @@ abstract contract PoSValidatorManager is
 
         // To prevent churn tracker abuse, check that one full churn period has passed,
         // so a delegator may not stake twice in the same churn period.
-        if (block.timestamp < delegator.startedAt + _getChurnPeriodSeconds()) {
+        // TODONOW: Is it safe to move this to initializeEndDelegation?
+        if (block.timestamp < delegator.startTime + _getChurnPeriodSeconds()) {
             revert MinStakeDurationNotPassed(uint64(block.timestamp));
         }
 
diff --git a/contracts/validator-manager/ValidatorManager.sol b/contracts/validator-manager/ValidatorManager.sol
index f7f39653f..3579cfd56 100644
--- a/contracts/validator-manager/ValidatorManager.sol
+++ b/contracts/validator-manager/ValidatorManager.sol
@@ -7,16 +7,19 @@ pragma solidity 0.8.25;
 
 import {ValidatorMessages} from "./ValidatorMessages.sol";
 import {
-    InitialValidator,
     IValidatorManager,
+    ValidatorChurnPeriod,
+    ValidatorManagerSettings,
+    ValidatorRegistrationInput
+} from "./interfaces/IValidatorManager.sol";
+import {
+    ACP99Manager,
+    InitialValidator,
     PChainOwner,
     ConversionData,
     Validator,
-    ValidatorChurnPeriod,
-    ValidatorManagerSettings,
-    ValidatorRegistrationInput,
     ValidatorStatus
-} from "./interfaces/IValidatorManager.sol";
+} from "./ACP99Manager.sol";
 import {
     IWarpMessenger,
     WarpMessage
@@ -31,7 +34,7 @@ import {Initializable} from
  *
  * @custom:security-contact https://github.com/ava-labs/icm-contracts/blob/main/SECURITY.md
  */
-abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValidatorManager {
+abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValidatorManager, ACP99Manager {
     // solhint-disable private-vars-leading-underscore
     /// @custom:storage-location erc7201:avalanche-icm.storage.ValidatorManager
 
@@ -78,6 +81,7 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
     error InvalidTotalWeight(uint64 weight);
     error InvalidValidationID(bytes32 validationID);
     error InvalidValidatorStatus(ValidatorStatus status);
+    error InvalidNonce(uint64 nonce);
     error InvalidWarpMessage();
     error MaxChurnRateExceeded(uint64 churnAmount);
     error NodeAlreadyRegistered(bytes nodeID);
@@ -144,12 +148,12 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
     }
 
     /**
-     * @notice See {IValidatorManager-initializeValidatorSet}.
+     * @notice See {ACP99Manager-initializeValidatorSet}.
      */
     function initializeValidatorSet(
         ConversionData calldata conversionData,
         uint32 messageIndex
-    ) external {
+    ) virtual public override {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
         if ($._initializedValidatorSet) {
             revert InvalidInitializationStatus();
@@ -182,10 +186,10 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
             $._validationPeriods[validationID].status = ValidatorStatus.Active;
             $._validationPeriods[validationID].nodeID = initialValidator.nodeID;
             $._validationPeriods[validationID].startingWeight = initialValidator.weight;
-            $._validationPeriods[validationID].messageNonce = 0;
+            $._validationPeriods[validationID].sentNonce = 0;
             $._validationPeriods[validationID].weight = initialValidator.weight;
-            $._validationPeriods[validationID].startedAt = uint64(block.timestamp);
-            $._validationPeriods[validationID].endedAt = 0;
+            $._validationPeriods[validationID].startTime = uint64(block.timestamp);
+            $._validationPeriods[validationID].endTime = 0;
             totalWeight += initialValidator.weight;
 
             emit InitialValidatorCreated(
@@ -213,7 +217,7 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
         $._initializedValidatorSet = true;
     }
 
-    function _validatePChainOwner(PChainOwner calldata pChainOwner) internal pure {
+    function _validatePChainOwner(PChainOwner memory pChainOwner) internal pure {
         // If threshold is 0, addresses must be empty.
         if (pChainOwner.threshold == 0 && pChainOwner.addresses.length != 0) {
             revert InvalidPChainOwnerThreshold(pChainOwner.threshold, pChainOwner.addresses.length);
@@ -235,20 +239,23 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
      * @notice Begins the validator registration process, and sets the initial weight for the validator.
      * This is the only method related to validator registration and removal that needs the initializedValidatorSet
      * modifier. All others are guarded by checking the validator status changes initialized in this function.
-     * @param input The inputs for a validator registration.
      * @param weight The weight of the validator being registered.
      */
-    function _initializeValidatorRegistration(
-        ValidatorRegistrationInput calldata input,
+    function _initiateValidatorRegistration(
+        bytes memory nodeID,
+        bytes memory blsPublicKey,
+        uint64 registrationExpiry,
+        PChainOwner memory remainingBalanceOwner,
+        PChainOwner memory disableOwner,
         uint64 weight
-    ) internal virtual initializedValidatorSet returns (bytes32) {
+    ) virtual override internal initializedValidatorSet returns (bytes32) {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
 
         if (
-            input.registrationExpiry <= block.timestamp
-                || input.registrationExpiry >= block.timestamp + MAXIMUM_REGISTRATION_EXPIRY_LENGTH
+            registrationExpiry <= block.timestamp
+                || registrationExpiry >= block.timestamp + MAXIMUM_REGISTRATION_EXPIRY_LENGTH
         ) {
-            revert InvalidRegistrationExpiry(input.registrationExpiry);
+            revert InvalidRegistrationExpiry(registrationExpiry);
         }
 
         // Ensure the new validator doesn't overflow the total weight
@@ -256,19 +263,19 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
             revert InvalidTotalWeight(weight);
         }
 
-        _validatePChainOwner(input.remainingBalanceOwner);
-        _validatePChainOwner(input.disableOwner);
+        _validatePChainOwner(remainingBalanceOwner);
+        _validatePChainOwner(disableOwner);
 
         // Ensure the nodeID is not the zero address, and is not already an active validator.
 
-        if (input.blsPublicKey.length != BLS_PUBLIC_KEY_LENGTH) {
-            revert InvalidBLSKeyLength(input.blsPublicKey.length);
+        if (blsPublicKey.length != BLS_PUBLIC_KEY_LENGTH) {
+            revert InvalidBLSKeyLength(blsPublicKey.length);
         }
-        if (input.nodeID.length == 0) {
-            revert InvalidNodeID(input.nodeID);
+        if (nodeID.length == 0) {
+            revert InvalidNodeID(nodeID);
         }
-        if ($._registeredValidators[input.nodeID] != bytes32(0)) {
-            revert NodeAlreadyRegistered(input.nodeID);
+        if ($._registeredValidators[nodeID] != bytes32(0)) {
+            revert NodeAlreadyRegistered(nodeID);
         }
 
         // Check that adding this validator would not exceed the maximum churn rate.
@@ -278,29 +285,29 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
             .packRegisterL1ValidatorMessage(
             ValidatorMessages.ValidationPeriod({
                 subnetID: $._subnetID,
-                nodeID: input.nodeID,
-                blsPublicKey: input.blsPublicKey,
-                remainingBalanceOwner: input.remainingBalanceOwner,
-                disableOwner: input.disableOwner,
-                registrationExpiry: input.registrationExpiry,
+                nodeID: nodeID,
+                blsPublicKey: blsPublicKey,
+                remainingBalanceOwner: remainingBalanceOwner,
+                disableOwner: disableOwner,
+                registrationExpiry: registrationExpiry,
                 weight: weight
             })
         );
         $._pendingRegisterValidationMessages[validationID] = registerL1ValidatorMessage;
-        $._registeredValidators[input.nodeID] = validationID;
+        $._registeredValidators[nodeID] = validationID;
 
         // Submit the message to the Warp precompile.
         bytes32 messageID = WARP_MESSENGER.sendWarpMessage(registerL1ValidatorMessage);
         $._validationPeriods[validationID].status = ValidatorStatus.PendingAdded;
-        $._validationPeriods[validationID].nodeID = input.nodeID;
+        $._validationPeriods[validationID].nodeID = nodeID;
         $._validationPeriods[validationID].startingWeight = weight;
-        $._validationPeriods[validationID].messageNonce = 0;
+        $._validationPeriods[validationID].sentNonce = 0;
         $._validationPeriods[validationID].weight = weight;
-        $._validationPeriods[validationID].startedAt = 0; // The validation period only starts once the registration is acknowledged.
-        $._validationPeriods[validationID].endedAt = 0;
+        $._validationPeriods[validationID].startTime = 0; // The validation period only starts once the registration is acknowledged.
+        $._validationPeriods[validationID].endTime = 0;
 
         emit ValidationPeriodCreated(
-            validationID, input.nodeID, messageID, weight, input.registrationExpiry
+            validationID, nodeID, messageID, weight, registrationExpiry
         );
 
         return validationID;
@@ -324,9 +331,9 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
     }
 
     /**
-     * @notice See {IValidatorManager-completeValidatorRegistration}.
+     * @notice See {ACP99Manager-completeValidatorRegistration}.
      */
-    function completeValidatorRegistration(uint32 messageIndex) external {
+    function completeValidatorRegistration(uint32 messageIndex) virtual public override returns (bytes32) {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
         (bytes32 validationID, bool validRegistration) = ValidatorMessages
             .unpackL1ValidatorRegistrationMessage(_getPChainWarpMessage(messageIndex).payload);
@@ -344,10 +351,12 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
 
         delete $._pendingRegisterValidationMessages[validationID];
         $._validationPeriods[validationID].status = ValidatorStatus.Active;
-        $._validationPeriods[validationID].startedAt = uint64(block.timestamp);
+        $._validationPeriods[validationID].startTime = uint64(block.timestamp);
         emit ValidationPeriodRegistered(
             validationID, $._validationPeriods[validationID].weight, block.timestamp
         );
+
+        return validationID;
     }
 
     /**
@@ -363,21 +372,49 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
      * @notice Returns a validator registered to the given validationID
      * @param validationID ID of the validation period associated with the validator
      */
-    function getValidator(bytes32 validationID) public view returns (Validator memory) {
+    function getValidator(bytes32 validationID) virtual override public view returns (Validator memory) {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
         return $._validationPeriods[validationID];
     }
 
+    function l1TotalWeight() virtual override public view returns (uint64) {
+        return _getValidatorManagerStorage()._churnTracker.totalWeight;
+    }
+
+    function subnetID() virtual override public view returns (bytes32) {
+        return _getValidatorManagerStorage()._subnetID;
+    }
+
+    function completeValidatorWeightUpdate(
+        uint32 messageIndex
+    ) virtual override public returns (bytes32) {
+        WarpMessage memory warpMessage = _getPChainWarpMessage(messageIndex);
+        (bytes32 validationID, uint64 nonce,) =
+            ValidatorMessages.unpackL1ValidatorWeightMessage(warpMessage.payload);
+        
+        ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
+
+        // The received nonce should be no greater than the highest sent nonce to ensure
+        // that weight changes are only initiated by this contract.
+        if ($._validationPeriods[validationID].sentNonce < nonce) {
+            revert InvalidNonce(nonce);
+        }
+
+        $._validationPeriods[validationID].receivedNonce = nonce;
+        
+        return validationID;
+    }
+
     /**
      * @notice Begins the process of ending an active validation period. The validation period must have been previously
      * started by a successful call to {completeValidatorRegistration} with the given validationID.
      * Any rewards for this validation period will stop accruing when this function is called.
      * @param validationID The ID of the validation period being ended.
      */
-    function _initializeEndValidation(bytes32 validationID)
+    function _initiateValidatorRemoval(bytes32 validationID)
         internal
         virtual
-        returns (Validator memory)
+        override
     {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
 
@@ -394,17 +431,15 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
 
         // Set the end time of the validation period, since it is no longer known to be an active validator
         // on the P-Chain.
-        validator.endedAt = uint64(block.timestamp);
+        validator.endTime = uint64(block.timestamp);
 
         // Save the validator updates.
         $._validationPeriods[validationID] = validator;
 
-        (, bytes32 messageID) = _setValidatorWeight(validationID, 0);
+        (, bytes32 messageID) = _initiateValidatorWeightUpdate(validationID, 0);
 
         // Emit the event to signal the start of the validator removal process.
         emit ValidatorRemovalInitialized(validationID, messageID, validator.weight, block.timestamp);
-
-        return validator;
     }
 
     /**
@@ -420,7 +455,7 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
         }
 
         WARP_MESSENGER.sendWarpMessage(
-            ValidatorMessages.packL1ValidatorWeightMessage(validationID, validator.messageNonce, 0)
+            ValidatorMessages.packL1ValidatorWeightMessage(validationID, validator.sentNonce, 0)
         );
     }
 
@@ -474,9 +509,9 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
         return (validationID, validator);
     }
 
-    function _incrementAndGetNonce(bytes32 validationID) internal returns (uint64) {
+    function _incrementSentNonce(bytes32 validationID) internal returns (uint64) {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
-        return ++$._validationPeriods[validationID].messageNonce;
+        return ++$._validationPeriods[validationID].sentNonce;
     }
 
     function _getPChainWarpMessage(uint32 messageIndex)
@@ -500,17 +535,17 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
         return warpMessage;
     }
 
-    function _setValidatorWeight(
+    function _initiateValidatorWeightUpdate(
         bytes32 validationID,
         uint64 newWeight
-    ) internal returns (uint64, bytes32) {
+    ) virtual override internal returns (uint64, bytes32) {
         ValidatorManagerStorage storage $ = _getValidatorManagerStorage();
         uint64 validatorWeight = $._validationPeriods[validationID].weight;
 
         // Check that changing the validator weight would not exceed the maximum churn rate.
         _checkAndUpdateChurnTracker(newWeight, validatorWeight);
 
-        uint64 nonce = _incrementAndGetNonce(validationID);
+        uint64 nonce = _incrementSentNonce(validationID);
 
         $._validationPeriods[validationID].weight = newWeight;
 
@@ -555,11 +590,11 @@ abstract contract ValidatorManager is Initializable, ContextUpgradeable, IValida
         ValidatorChurnPeriod memory churnTracker = $._churnTracker;
 
         if (
-            churnTracker.startedAt == 0
-                || currentTime >= churnTracker.startedAt + $._churnPeriodSeconds
+            churnTracker.startTime == 0
+                || currentTime >= churnTracker.startTime + $._churnPeriodSeconds
         ) {
             churnTracker.churnAmount = weightChange;
-            churnTracker.startedAt = currentTime;
+            churnTracker.startTime = currentTime;
             churnTracker.initialWeight = churnTracker.totalWeight;
         } else {
             // Churn is always additive whether the weight is being added or removed.
diff --git a/contracts/validator-manager/interfaces/IPoSValidatorManager.sol b/contracts/validator-manager/interfaces/IPoSValidatorManager.sol
index 841f7d362..59cd0b311 100644
--- a/contracts/validator-manager/interfaces/IPoSValidatorManager.sol
+++ b/contracts/validator-manager/interfaces/IPoSValidatorManager.sol
@@ -52,7 +52,7 @@ struct Delegator {
     address owner;
     bytes32 validationID;
     uint64 weight;
-    uint64 startedAt;
+    uint64 startTime;
     uint64 startingNonce;
     uint64 endingNonce;
 }
diff --git a/contracts/validator-manager/interfaces/IValidatorManager.sol b/contracts/validator-manager/interfaces/IValidatorManager.sol
index 9ee1ed6ab..37001c44a 100644
--- a/contracts/validator-manager/interfaces/IValidatorManager.sol
+++ b/contracts/validator-manager/interfaces/IValidatorManager.sol
@@ -5,45 +5,13 @@
 
 pragma solidity 0.8.25;
 
-/**
- * @dev Validator status
- */
-enum ValidatorStatus {
-    Unknown,
-    PendingAdded,
-    Active,
-    PendingRemoved,
-    Completed,
-    Invalidated
-}
-
-/**
- * @dev Specifies the owner of a validator's remaining balance or disable owner on the P-Chain.
- * P-Chain addresses are also 20-bytes, so we use the address type to represent them.
- */
-struct PChainOwner {
-    uint32 threshold;
-    address[] addresses;
-}
-
-/**
- * @dev Contains the active state of a Validator
- */
-struct Validator {
-    ValidatorStatus status;
-    bytes nodeID;
-    uint64 startingWeight;
-    uint64 messageNonce;
-    uint64 weight;
-    uint64 startedAt;
-    uint64 endedAt;
-}
+import {ValidatorStatus, ConversionData, PChainOwner} from "../ACP99Manager.sol";
 
 /**
  * @dev Describes the current churn period
  */
 struct ValidatorChurnPeriod {
-    uint256 startedAt;
+    uint256 startTime;
     uint64 initialWeight;
     uint64 totalWeight;
     uint64 churnAmount;
@@ -61,28 +29,6 @@ struct ValidatorManagerSettings {
     uint8 maximumChurnPercentage;
 }
 
-/**
- * @dev Description of the conversion data used to convert
- * a subnet to an L1 on the P-Chain.
- * This data is the pre-image of a hash that is authenticated by the P-Chain
- * and verified by the Validator Manager.
- */
-struct ConversionData {
-    bytes32 subnetID;
-    bytes32 validatorManagerBlockchainID;
-    address validatorManagerAddress;
-    InitialValidator[] initialValidators;
-}
-
-/**
- * @dev Specifies an initial validator, used in the conversion data.
- */
-struct InitialValidator {
-    bytes nodeID;
-    bytes blsPublicKey;
-    uint64 weight;
-}
-
 /**
  * @dev Specifies a validator to register.
  */
@@ -171,16 +117,6 @@ interface IValidatorManager {
         bytes32 setWeightMessageID
     );
 
-    /**
-     * @notice Verifies and sets the initial validator set for the chain through a P-Chain SubnetToL1ConversionMessage.
-     * @param conversionData The subnet conversion message data used to recompute and verify against the conversionID.
-     * @param messsageIndex The index that contains the SubnetToL1ConversionMessage ICM message containing the conversionID to be verified against the provided {ConversionData}
-     */
-    function initializeValidatorSet(
-        ConversionData calldata conversionData,
-        uint32 messsageIndex
-    ) external;
-
     /**
      * @notice Resubmits a validator registration message to be sent to the P-Chain.
      * Only necessary if the original message can't be delivered due to validator churn.
@@ -188,28 +124,10 @@ interface IValidatorManager {
      */
     function resendRegisterValidatorMessage(bytes32 validationID) external;
 
-    /**
-     * @notice Completes the validator registration process by returning an acknowledgement of the registration of a
-     * validationID from the P-Chain.
-     * @param messageIndex The index of the ICM message to be received providing the acknowledgement.
-     */
-    function completeValidatorRegistration(uint32 messageIndex) external;
-
     /**
      * @notice Resubmits a validator end message to be sent to the P-Chain.
      * Only necessary if the original message can't be delivered due to validator churn.
      * @param validationID The ID of the validation period being ended.
      */
     function resendEndValidatorMessage(bytes32 validationID) external;
-
-    /**
-     * @notice Completes the process of ending a validation period by receiving an acknowledgement from the P-Chain
-     * that the validation ID is not active and will never be active in the future. Returns the the stake associated
-     * with the validation.
-     * Note: This function can be used for successful validation periods that have been explicitly ended by calling
-     * {initializeEndValidation} or for validation periods that never began on the P-Chain due to the {registrationExpiry} being reached.
-     * @param messageIndex The index of the ICM message to be received providing the proof the validation is not active
-     * and never will be active on the P-Chain.
-     */
-    function completeEndValidation(uint32 messageIndex) external;
 }