diff --git a/src/google/adk/auth/auth_handler.py b/src/google/adk/auth/auth_handler.py
index 07515ab2e8..3248cbe11f 100644
--- a/src/google/adk/auth/auth_handler.py
+++ b/src/google/adk/auth/auth_handler.py
@@ -48,9 +48,10 @@ async def exchange_auth_token(
       self,
   ) -> AuthCredential:
     exchanger = OAuth2CredentialExchanger()
-    return await exchanger.exchange(
+    exchanged_credential, _ = await exchanger.exchange(
         self.auth_config.exchanged_auth_credential, self.auth_config.auth_scheme
     )
+    return exchanged_credential
 
   async def parse_and_store_auth_response(self, state: State) -> None:
 
diff --git a/src/google/adk/auth/credential_manager.py b/src/google/adk/auth/credential_manager.py
index c022ab694c..292963e151 100644
--- a/src/google/adk/auth/credential_manager.py
+++ b/src/google/adk/auth/credential_manager.py
@@ -214,15 +214,14 @@ async def _exchange_credential(
       return credential, False
 
     if isinstance(exchanger, ServiceAccountCredentialExchanger):
-      exchanged_credential = exchanger.exchange_credential(
-          self._auth_config.auth_scheme, credential
-      )
-    else:
-      exchanged_credential = await exchanger.exchange(
-          credential, self._auth_config.auth_scheme
+      return (
+          exchanger.exchange_credential(
+              self._auth_config.auth_scheme, credential
+          ),
+          True,
       )
 
-    return exchanged_credential, True
+    return await exchanger.exchange(credential, self._auth_config.auth_scheme)
 
   async def _refresh_credential(
       self, credential: AuthCredential
diff --git a/src/google/adk/auth/exchanger/base_credential_exchanger.py b/src/google/adk/auth/exchanger/base_credential_exchanger.py
index 31106b55e2..2b686d6681 100644
--- a/src/google/adk/auth/exchanger/base_credential_exchanger.py
+++ b/src/google/adk/auth/exchanger/base_credential_exchanger.py
@@ -41,7 +41,7 @@ async def exchange(
       self,
       auth_credential: AuthCredential,
       auth_scheme: Optional[AuthScheme] = None,
-  ) -> AuthCredential:
+  ) -> tuple[AuthCredential, bool]:
     """Exchange credential if needed.
 
     Args:
@@ -49,7 +49,10 @@ async def exchange(
         auth_scheme: The authentication scheme (optional, some exchangers don't need it).
 
     Returns:
-        The exchanged credential.
+        A tuple of (credential, exchanged) where:
+        - credential: The exchanged credential if exchange occurred, otherwise
+          the original credential.
+        - exchanged: True if credential was exchanged, False otherwise.
 
     Raises:
         CredentialExchangeError: If credential exchange fails.
diff --git a/src/google/adk/auth/exchanger/oauth2_credential_exchanger.py b/src/google/adk/auth/exchanger/oauth2_credential_exchanger.py
index 431798cc6c..e4b392abde 100644
--- a/src/google/adk/auth/exchanger/oauth2_credential_exchanger.py
+++ b/src/google/adk/auth/exchanger/oauth2_credential_exchanger.py
@@ -51,7 +51,7 @@ async def exchange(
       self,
       auth_credential: AuthCredential,
       auth_scheme: Optional[AuthScheme] = None,
-  ) -> AuthCredential:
+  ) -> tuple[AuthCredential, bool]:
     """Exchange OAuth2 credential from authorization response.
 
     if credential exchange failed, the original credential will be returned.
@@ -61,7 +61,10 @@ async def exchange(
         auth_scheme: The OAuth2 authentication scheme.
 
     Returns:
-        The exchanged credential with access token.
+        A tuple of (credential, exchanged) where:
+        - credential: The exchanged credential with an access token if exchange occurred, otherwise
+          the original credential.
+        - exchanged: True if credential was exchanged, False otherwise.
 
     Raises:
         CredentialExchangeError: If auth_scheme is missing.
@@ -79,10 +82,10 @@ async def exchange(
       logger.warning(
           "authlib is not available, skipping OAuth2 credential exchange."
       )
-      return auth_credential
+      return (auth_credential, False)
 
     if auth_credential.oauth2 and auth_credential.oauth2.access_token:
-      return auth_credential
+      return (auth_credential, False)
 
     # Determine grant type from auth_scheme
     grant_type = self._determine_grant_type(auth_scheme)
@@ -97,7 +100,7 @@ async def exchange(
       )
     else:
       logger.warning("Unsupported OAuth2 grant type: %s", grant_type)
-      return auth_credential
+      return auth_credential, False
 
   def _determine_grant_type(
       self, auth_scheme: AuthScheme
@@ -129,7 +132,7 @@ async def _exchange_client_credentials(
       self,
       auth_credential: AuthCredential,
       auth_scheme: AuthScheme,
-  ) -> AuthCredential:
+  ) -> tuple[AuthCredential, bool]:
     """Exchange client credentials for access token.
 
     Args:
@@ -137,14 +140,17 @@ async def _exchange_client_credentials(
         auth_scheme: The OAuth2 authentication scheme.
 
     Returns:
-        The credential with access token.
+        A tuple of (credential, exchanged) where:
+        - credential: The exchanged credential with an access token if exchange occurred, otherwise
+          the original credential.
+        - exchanged: True if credential was exchanged, False otherwise.
     """
     client, token_endpoint = create_oauth2_session(auth_scheme, auth_credential)
     if not client:
       logger.warning(
           "Could not create OAuth2 session for client credentials exchange"
       )
-      return auth_credential
+      return auth_credential, False
 
     try:
       tokens = client.fetch_token(
@@ -155,9 +161,9 @@ async def _exchange_client_credentials(
       logger.debug("Successfully exchanged client credentials for access token")
     except Exception as e:
       logger.error("Failed to exchange client credentials: %s", e)
-      return auth_credential
+      return auth_credential, False
 
-    return auth_credential
+    return auth_credential, True
 
   def _normalize_auth_uri(self, auth_uri: str | None) -> str | None:
     # Authlib currently used a simplified token check by simply scanning hash existence,
@@ -171,7 +177,7 @@ async def _exchange_authorization_code(
       self,
       auth_credential: AuthCredential,
       auth_scheme: AuthScheme,
-  ) -> AuthCredential:
+  ) -> tuple[AuthCredential, bool]:
     """Exchange authorization code for access token.
 
     Args:
@@ -179,14 +185,17 @@ async def _exchange_authorization_code(
         auth_scheme: The OAuth2 authentication scheme.
 
     Returns:
-        The credential with access token.
+        A tuple of (credential, exchanged) where:
+        - credential: The exchanged credential with an access token if exchange occurred, otherwise
+          the original credential.
+        - exchanged: True if credential was exchanged, False otherwise.
     """
     client, token_endpoint = create_oauth2_session(auth_scheme, auth_credential)
     if not client:
       logger.warning(
           "Could not create OAuth2 session for authorization code exchange"
       )
-      return auth_credential
+      return auth_credential, False
 
     try:
       tokens = client.fetch_token(
@@ -201,6 +210,6 @@ async def _exchange_authorization_code(
       logger.debug("Successfully exchanged authorization code for access token")
     except Exception as e:
       logger.error("Failed to exchange authorization code: %s", e)
-      return auth_credential
+      return auth_credential, False
 
-    return auth_credential
+    return auth_credential, True
diff --git a/tests/unittests/auth/exchanger/test_oauth2_credential_exchanger.py b/tests/unittests/auth/exchanger/test_oauth2_credential_exchanger.py
index 4fc439ad13..284a911270 100644
--- a/tests/unittests/auth/exchanger/test_oauth2_credential_exchanger.py
+++ b/tests/unittests/auth/exchanger/test_oauth2_credential_exchanger.py
@@ -33,7 +33,6 @@
 class TestOAuth2CredentialExchanger:
   """Test suite for OAuth2CredentialExchanger."""
 
-  @pytest.mark.asyncio
   async def test_exchange_with_existing_token(self):
     """Test exchange method when access token already exists."""
     scheme = OpenIdConnectWithConfig(
@@ -55,14 +54,16 @@ async def test_exchange_with_existing_token(self):
     )
 
     exchanger = OAuth2CredentialExchanger()
-    result = await exchanger.exchange(credential, scheme)
+    exchanged_credential, was_exchanged = await exchanger.exchange(
+        credential, scheme
+    )
 
     # Should return the same credential since access token already exists
-    assert result == credential
-    assert result.oauth2.access_token == "existing_token"
+    assert exchanged_credential == credential
+    assert exchanged_credential.oauth2.access_token == "existing_token"
+    assert not was_exchanged
 
   @patch("google.adk.auth.oauth2_credential_util.OAuth2Session")
-  @pytest.mark.asyncio
   async def test_exchange_success(self, mock_oauth2_session):
     """Test successful token exchange."""
     # Setup mock
@@ -96,14 +97,16 @@ async def test_exchange_success(self, mock_oauth2_session):
     )
 
     exchanger = OAuth2CredentialExchanger()
-    result = await exchanger.exchange(credential, scheme)
+    exchanged_credential, was_exchanged = await exchanger.exchange(
+        credential, scheme
+    )
 
     # Verify token exchange was successful
-    assert result.oauth2.access_token == "new_access_token"
-    assert result.oauth2.refresh_token == "new_refresh_token"
+    assert exchanged_credential.oauth2.access_token == "new_access_token"
+    assert exchanged_credential.oauth2.refresh_token == "new_refresh_token"
+    assert was_exchanged
     mock_client.fetch_token.assert_called_once()
 
-  @pytest.mark.asyncio
   async def test_exchange_missing_auth_scheme(self):
     """Test exchange with missing auth_scheme raises ValueError."""
     credential = AuthCredential(
@@ -122,7 +125,6 @@ async def test_exchange_missing_auth_scheme(self):
       assert "auth_scheme is required" in str(e)
 
   @patch("google.adk.auth.oauth2_credential_util.OAuth2Session")
-  @pytest.mark.asyncio
   async def test_exchange_no_session(self, mock_oauth2_session):
     """Test exchange when OAuth2Session cannot be created."""
     # Mock to return None for create_oauth2_session
@@ -146,14 +148,16 @@ async def test_exchange_no_session(self, mock_oauth2_session):
     )
 
     exchanger = OAuth2CredentialExchanger()
-    result = await exchanger.exchange(credential, scheme)
+    exchanged_credential, was_exchanged = await exchanger.exchange(
+        credential, scheme
+    )
 
     # Should return original credential when session creation fails
-    assert result == credential
-    assert result.oauth2.access_token is None
+    assert exchanged_credential == credential
+    assert exchanged_credential.oauth2.access_token is None
+    assert not was_exchanged
 
   @patch("google.adk.auth.oauth2_credential_util.OAuth2Session")
-  @pytest.mark.asyncio
   async def test_exchange_fetch_token_failure(self, mock_oauth2_session):
     """Test exchange when fetch_token fails."""
     # Setup mock to raise exception during fetch_token
@@ -181,14 +185,16 @@ async def test_exchange_fetch_token_failure(self, mock_oauth2_session):
     )
 
     exchanger = OAuth2CredentialExchanger()
-    result = await exchanger.exchange(credential, scheme)
+    exchanged_credential, was_exchanged = await exchanger.exchange(
+        credential, scheme
+    )
 
     # Should return original credential when fetch_token fails
-    assert result == credential
-    assert result.oauth2.access_token is None
+    assert exchanged_credential == credential
+    assert exchanged_credential.oauth2.access_token is None
+    assert not was_exchanged
     mock_client.fetch_token.assert_called_once()
 
-  @pytest.mark.asyncio
   async def test_exchange_authlib_not_available(self):
     """Test exchange when authlib is not available."""
     scheme = OpenIdConnectWithConfig(
@@ -217,14 +223,16 @@ async def test_exchange_authlib_not_available(self):
         "google.adk.auth.exchanger.oauth2_credential_exchanger.AUTHLIB_AVAILABLE",
         False,
     ):
-      result = await exchanger.exchange(credential, scheme)
+      exchanged_credential, was_exchanged = await exchanger.exchange(
+          credential, scheme
+      )
 
     # Should return original credential when authlib is not available
-    assert result == credential
-    assert result.oauth2.access_token is None
+    assert exchanged_credential == credential
+    assert exchanged_credential.oauth2.access_token is None
+    assert not was_exchanged
 
   @patch("google.adk.auth.oauth2_credential_util.OAuth2Session")
-  @pytest.mark.asyncio
   async def test_exchange_client_credentials_success(self, mock_oauth2_session):
     """Test successful client credentials exchange."""
     # Setup mock
@@ -255,17 +263,19 @@ async def test_exchange_client_credentials_success(self, mock_oauth2_session):
     )
 
     exchanger = OAuth2CredentialExchanger()
-    result = await exchanger.exchange(credential, scheme)
+    exchanged_credential, was_exchanged = await exchanger.exchange(
+        credential, scheme
+    )
 
     # Verify client credentials exchange was successful
-    assert result.oauth2.access_token == "client_access_token"
+    assert exchanged_credential.oauth2.access_token == "client_access_token"
+    assert was_exchanged
     mock_client.fetch_token.assert_called_once_with(
         "https://example.com/token",
         grant_type="client_credentials",
     )
 
   @patch("google.adk.auth.oauth2_credential_util.OAuth2Session")
-  @pytest.mark.asyncio
   async def test_exchange_client_credentials_failure(self, mock_oauth2_session):
     """Test client credentials exchange failure."""
     # Setup mock to raise exception during fetch_token
@@ -292,15 +302,17 @@ async def test_exchange_client_credentials_failure(self, mock_oauth2_session):
     )
 
     exchanger = OAuth2CredentialExchanger()
-    result = await exchanger.exchange(credential, scheme)
+    exchanged_credential, was_exchanged = await exchanger.exchange(
+        credential, scheme
+    )
 
     # Should return original credential when client credentials exchange fails
-    assert result == credential
-    assert result.oauth2.access_token is None
+    assert exchanged_credential == credential
+    assert exchanged_credential.oauth2.access_token is None
+    assert not was_exchanged
     mock_client.fetch_token.assert_called_once()
 
   @patch("google.adk.auth.oauth2_credential_util.OAuth2Session")
-  @pytest.mark.asyncio
   async def test_exchange_normalize_uri(self, mock_oauth2_session):
     """Test exchange method normalizes auth_response_uri."""
     mock_client = Mock()
@@ -343,7 +355,6 @@ async def test_exchange_normalize_uri(self, mock_oauth2_session):
         grant_type=OAuthGrantType.AUTHORIZATION_CODE,
     )
 
-  @pytest.mark.asyncio
   async def test_determine_grant_type_client_credentials(self):
     """Test grant type determination for client credentials."""
     flows = OAuthFlows(
@@ -360,7 +371,6 @@ async def test_determine_grant_type_client_credentials(self):
 
     assert grant_type == OAuthGrantType.CLIENT_CREDENTIALS
 
-  @pytest.mark.asyncio
   async def test_determine_grant_type_openid_connect(self):
     """Test grant type determination for OpenID Connect (defaults to auth code)."""
     scheme = OpenIdConnectWithConfig(