diff --git a/packages/auth/src/core/auth/auth_impl.ts b/packages/auth/src/core/auth/auth_impl.ts
index 81ab6492f3f..fc98a258fca 100644
--- a/packages/auth/src/core/auth/auth_impl.ts
+++ b/packages/auth/src/core/auth/auth_impl.ts
@@ -676,7 +676,7 @@ export class AuthImpl implements AuthInternal, _FirebaseService {
     nextOrObserver: NextOrObserver<FirebaseToken>,
     error?: ErrorFn,
     completed?: CompleteFn
-  ): Unsubscribe | undefined {
+  ): Unsubscribe {
     return this.registerStateListener(
       this.firebaseTokenSubscription,
       nextOrObserver,
diff --git a/packages/auth/src/core/auth/firebase_internal.test.ts b/packages/auth/src/core/auth/firebase_internal.test.ts
index 5954412364e..9e3c606d890 100644
--- a/packages/auth/src/core/auth/firebase_internal.test.ts
+++ b/packages/auth/src/core/auth/firebase_internal.test.ts
@@ -327,6 +327,72 @@ describe('core/auth/firebase_internal - Regional Firebase Auth', () => {
     });
   });
 
+  context('addAuthTokenListener', () => {
+    let isProactiveRefresh = false;
+    const initialToken = 'initial-regional-token';
+    const updatedToken = 'updated-regional-token';
+    beforeEach(async () => {
+      isProactiveRefresh = false;
+
+      sinon
+        .stub(regionalAuth as any, '_startProactiveRefresh')
+        .callsFake(() => {
+          isProactiveRefresh = true;
+        });
+      sinon.stub(regionalAuth as any, '_stopProactiveRefresh').callsFake(() => {
+        isProactiveRefresh = false;
+      });
+      await regionalAuth._updateFirebaseToken({
+        token: initialToken,
+        expirationTime: now + 300_000
+      });
+    });
+
+    it('gets called with the current token (or null)', done => {
+      let firstCall = true;
+
+      regionalAuthInternal.addAuthTokenListener(token => {
+        if (firstCall) {
+          firstCall = false;
+          expect(token).to.eq(initialToken);
+          // eslint-disable-next-line @typescript-eslint/no-floating-promises
+          regionalAuth._updateFirebaseToken({
+            token: updatedToken,
+            expirationTime: now + 300_000
+          });
+          return;
+        }
+
+        expect(token).to.eq(updatedToken);
+        expect(isProactiveRefresh).to.be.true;
+        done();
+      });
+    });
+
+    it('gets called on subsequent updates', async () => {
+      let regionalCount = 0;
+      regionalAuthInternal.addAuthTokenListener(() => {
+        regionalCount++;
+      });
+
+      await regionalAuth.getFirebaseAccessToken();
+      await regionalAuth.getFirebaseAccessToken();
+      await regionalAuth.getFirebaseAccessToken();
+      await regionalAuth.getFirebaseAccessToken();
+
+      expect(regionalCount).to.eq(5);
+    });
+
+    it('errors if Regional Auth is not initialized', () => {
+      delete (regionalAuth as unknown as Record<string, unknown>)[
+        '_initializationPromise'
+      ];
+      expect(() =>
+        regionalAuthInternal.addAuthTokenListener(() => {})
+      ).to.throw(FirebaseError, 'auth/dependent-sdk-initialized-before-auth');
+    });
+  });
+
   context('getUid', () => {
     it('throws an error if regionalAuth is initialized', () => {
       expect(() => regionalAuthInternal.getUid()).to.throw(
diff --git a/packages/auth/src/core/auth/firebase_internal.ts b/packages/auth/src/core/auth/firebase_internal.ts
index 970e99fa4ec..e2e3ba928f0 100644
--- a/packages/auth/src/core/auth/firebase_internal.ts
+++ b/packages/auth/src/core/auth/firebase_internal.ts
@@ -18,7 +18,7 @@
 import { Unsubscribe } from '@firebase/util';
 import { FirebaseAuthInternal } from '@firebase/auth-interop-types';
 
-import { AuthInternal } from '../../model/auth';
+import { AuthInternal, FirebaseToken } from '../../model/auth';
 import { UserInternal } from '../../model/user';
 import { _assert } from '../util/assert';
 import { AuthErrorCode } from '../errors';
@@ -64,12 +64,28 @@ export class AuthInterop implements FirebaseAuthInternal {
       return;
     }
 
-    const unsubscribe = this.auth.onIdTokenChanged(user => {
-      listener(
-        (user as UserInternal | null)?.stsTokenManager.accessToken || null
+    let unsubscribe: Unsubscribe;
+    if (this.auth.tenantConfig) {
+      unsubscribe = this.auth.onFirebaseTokenChanged(
+        (firebaseToken: FirebaseToken | null) => {
+          try {
+            listener(firebaseToken?.token || null);
+          } catch (error) {
+            console.error('Failed to retrieve firebase token:', error);
+            listener(null);
+          }
+        }
       );
-    });
+    } else {
+      unsubscribe = this.auth.onIdTokenChanged(user => {
+        listener(
+          (user as UserInternal | null)?.stsTokenManager.accessToken || null
+        );
+      });
+    }
+
     this.internalListeners.set(listener, unsubscribe);
+    // TODO - b/455792813: Handle proactive refresh for R-GCIP Firebase Token.
     this.updateProactiveRefresh();
   }
 
diff --git a/packages/auth/src/model/auth.ts b/packages/auth/src/model/auth.ts
index 308231573b0..ef9373c3717 100644
--- a/packages/auth/src/model/auth.ts
+++ b/packages/auth/src/model/auth.ts
@@ -85,7 +85,7 @@ export interface AuthInternal extends Auth {
     nextOrObserver: NextOrObserver<FirebaseToken>,
     error?: ErrorFn,
     completed?: CompleteFn
-  ): Unsubscribe | undefined;
+  ): Unsubscribe;
   _agentRecaptchaConfig: RecaptchaConfig | null;
   _tenantRecaptchaConfigs: Record<string, RecaptchaConfig>;
   _projectPasswordPolicy: PasswordPolicy | null;