diff --git a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json
index 3748c3744f..e1381a9044 100644
--- a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json
+++ b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json
@@ -14,7 +14,8 @@
         "amr": null,
         "c_hash": "",
         "ext": {
-          "hooked": "legacy"
+          "hooked": "legacy",
+          "sid": ""
         }
       },
       "headers": {
diff --git a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json
index 3748c3744f..e1381a9044 100644
--- a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json
+++ b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json
@@ -14,7 +14,8 @@
         "amr": null,
         "c_hash": "",
         "ext": {
-          "hooked": "legacy"
+          "hooked": "legacy",
+          "sid": ""
         }
       },
       "headers": {
diff --git a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json
index 3748c3744f..e1381a9044 100644
--- a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json
+++ b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=jwt-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json
@@ -14,7 +14,8 @@
         "amr": null,
         "c_hash": "",
         "ext": {
-          "hooked": "legacy"
+          "hooked": "legacy",
+          "sid": ""
         }
       },
       "headers": {
diff --git a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json
index 3748c3744f..e1381a9044 100644
--- a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json
+++ b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=0-description=should_pass_request_if_strategy_passes-should_call_refresh_token_hook_if_configured-hook=new.json
@@ -14,7 +14,8 @@
         "amr": null,
         "c_hash": "",
         "ext": {
-          "hooked": "legacy"
+          "hooked": "legacy",
+          "sid": ""
         }
       },
       "headers": {
diff --git a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json
index 3748c3744f..e1381a9044 100644
--- a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json
+++ b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=2-description=should_pass_because_prompt=none_and_max_age_is_less_than_auth_time-should_call_refresh_token_hook_if_configured-hook=new.json
@@ -14,7 +14,8 @@
         "amr": null,
         "c_hash": "",
         "ext": {
-          "hooked": "legacy"
+          "hooked": "legacy",
+          "sid": ""
         }
       },
       "headers": {
diff --git a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json
index 3748c3744f..e1381a9044 100644
--- a/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json
+++ b/oauth2/.snapshots/TestAuthCodeWithMockStrategy-strategy=opaque-case=5-description=should_pass_with_prompt=login_when_authentication_time_is_recent-should_call_refresh_token_hook_if_configured-hook=new.json
@@ -14,7 +14,8 @@
         "amr": null,
         "c_hash": "",
         "ext": {
-          "hooked": "legacy"
+          "hooked": "legacy",
+          "sid": ""
         }
       },
       "headers": {
diff --git a/oauth2/token_hook.go b/oauth2/token_hook.go
index d32cadd7e4..83c7491aad 100644
--- a/oauth2/token_hook.go
+++ b/oauth2/token_hook.go
@@ -143,13 +143,26 @@ func executeHookAndUpdateSession(ctx context.Context, reg x.HTTPClientProvider,
 		)
 	}
 
-	// Overwrite existing session data (extra claims).
-	session.Extra = respBody.Session.AccessToken
+	// Update existing session data (extra claims).
+	session.Extra = updateExtraClaims(session.Extra, respBody.Session.AccessToken)
 	idTokenClaims := session.IDTokenClaims()
-	idTokenClaims.Extra = respBody.Session.IDToken
+	idTokenClaims.Extra = updateExtraClaims(idTokenClaims.Extra, respBody.Session.IDToken)
 	return nil
 }
 
+func updateExtraClaims(claimsToUpdate, webhookExtraClaims map[string]interface{}) map[string]interface{} {
+	if webhookExtraClaims == nil {
+		return claimsToUpdate
+	}
+	if claimsToUpdate == nil {
+		claimsToUpdate = make(map[string]interface{})
+	}
+	for key, value := range webhookExtraClaims {
+		claimsToUpdate[key] = value
+	}
+	return claimsToUpdate
+}
+
 // TokenHook is an AccessRequestHook called for all grant types.
 func TokenHook(reg interface {
 	config.Provider
diff --git a/oauth2/token_hook_test.go b/oauth2/token_hook_test.go
new file mode 100644
index 0000000000..d6c3dd24d6
--- /dev/null
+++ b/oauth2/token_hook_test.go
@@ -0,0 +1,111 @@
+// Copyright © 2024 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+package oauth2
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestUpdateExtraClaims(t *testing.T) {
+	tests := []struct {
+		name               string
+		priorExtraClaims   map[string]interface{}
+		webhookExtraClaims map[string]interface{}
+		expected           map[string]interface{}
+	}{
+		{
+			name: "Merge with no updates",
+			priorExtraClaims: map[string]interface{}{
+				"claim1": "value1",
+				"claim2": "value2",
+			},
+			webhookExtraClaims: map[string]interface{}{
+				"claim3": "value3",
+				"claim4": "value4",
+			},
+			expected: map[string]interface{}{
+				"claim1": "value1",
+				"claim2": "value2",
+				"claim3": "value3",
+				"claim4": "value4",
+			},
+		},
+		{
+			name: "Merge with updates",
+			priorExtraClaims: map[string]interface{}{
+				"claim1": "value1",
+				"claim2": "value2",
+			},
+			webhookExtraClaims: map[string]interface{}{
+				"claim2": "newValue2", // Overwrites prior claim2
+				"claim3": "value3",
+			},
+			expected: map[string]interface{}{
+				"claim1": "value1",
+				"claim2": "newValue2",
+				"claim3": "value3",
+			},
+		},
+		{
+			name: "Empty webhook claims",
+			priorExtraClaims: map[string]interface{}{
+				"claim1": "value1",
+			},
+			webhookExtraClaims: map[string]interface{}{},
+			expected: map[string]interface{}{
+				"claim1": "value1",
+			},
+		},
+		{
+			name:             "Empty prior claims",
+			priorExtraClaims: map[string]interface{}{},
+			webhookExtraClaims: map[string]interface{}{
+				"claim1": "value1",
+			},
+			expected: map[string]interface{}{
+				"claim1": "value1",
+			},
+		},
+		{
+			name:               "Both maps empty",
+			priorExtraClaims:   map[string]interface{}{},
+			webhookExtraClaims: map[string]interface{}{},
+			expected:           map[string]interface{}{},
+		},
+		{
+			name:               "Nil webhook claims",
+			priorExtraClaims:   map[string]interface{}{"claim1": "value1"},
+			webhookExtraClaims: nil,
+			expected:           map[string]interface{}{"claim1": "value1"},
+		},
+		{
+			name:               "Nil prior claims",
+			priorExtraClaims:   nil,
+			webhookExtraClaims: map[string]interface{}{"claim1": "value1"},
+			expected:           map[string]interface{}{"claim1": "value1"},
+		},
+		{
+			name:               "Both maps nil",
+			priorExtraClaims:   nil,
+			webhookExtraClaims: nil,
+			expected:           nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Act
+			if tt.priorExtraClaims == nil {
+				tt.priorExtraClaims = nil // Explicitly ensure nil for this test case
+			}
+			actual := updateExtraClaims(tt.priorExtraClaims, tt.webhookExtraClaims)
+
+			// Assert
+			if !reflect.DeepEqual(actual, tt.expected) {
+				t.Errorf("claimsToUpdate = %v, want %v", tt.priorExtraClaims, tt.expected)
+			}
+		})
+	}
+}