diff --git a/packages/google-api-core/tests/asyncio/test_grpc_helpers_async.py b/packages/google-api-core/tests/asyncio/test_grpc_helpers_async.py
index 0855e15e9ec7..dcb09f18fea2 100644
--- a/packages/google-api-core/tests/asyncio/test_grpc_helpers_async.py
+++ b/packages/google-api-core/tests/asyncio/test_grpc_helpers_async.py
@@ -421,9 +421,15 @@ def test_create_channel_implicit_with_default_host(
     assert channel is grpc_secure_channel.return_value
 
     google_auth_default.assert_called_once_with(scopes=None, default_scopes=None)
-    auth_metadata_plugin.assert_called_once_with(
-        mock.sentinel.credentials, mock.sentinel.Request, default_host=default_host
-    )
+    assert auth_metadata_plugin.call_count == 1
+    assert auth_metadata_plugin.call_args.args == (
+        mock.sentinel.credentials,
+        mock.sentinel.Request,
+    )
+    assert auth_metadata_plugin.call_args.kwargs["default_host"] == default_host
+    # google-auth >= 2.56.3 supports suppress_metrics_header; older versions omit it during fallback
+    if "suppress_metrics_header" in auth_metadata_plugin.call_args.kwargs:
+        assert auth_metadata_plugin.call_args.kwargs["suppress_metrics_header"] is True
     grpc_secure_channel.assert_called_once_with(
         expected_target, composite_creds, compression=None
     )
diff --git a/packages/google-api-core/tests/unit/test_grpc_helpers.py b/packages/google-api-core/tests/unit/test_grpc_helpers.py
index 4f2912f82367..69281d58109b 100644
--- a/packages/google-api-core/tests/unit/test_grpc_helpers.py
+++ b/packages/google-api-core/tests/unit/test_grpc_helpers.py
@@ -453,9 +453,15 @@ def test_create_channel_implicit_with_default_host(
     assert channel is grpc_secure_channel.return_value
 
     google_auth_default.assert_called_once_with(scopes=None, default_scopes=None)
-    auth_metadata_plugin.assert_called_once_with(
-        mock.sentinel.credentials, mock.sentinel.Request, default_host=default_host
+    assert auth_metadata_plugin.call_count == 1
+    assert auth_metadata_plugin.call_args.args == (
+        mock.sentinel.credentials,
+        mock.sentinel.Request,
     )
+    assert auth_metadata_plugin.call_args.kwargs["default_host"] == default_host
+    # google-auth >= 2.56.3 supports suppress_metrics_header; older versions omit it during fallback
+    if "suppress_metrics_header" in auth_metadata_plugin.call_args.kwargs:
+        assert auth_metadata_plugin.call_args.kwargs["suppress_metrics_header"] is True
 
     grpc_secure_channel.assert_called_once_with(
         expected_target, composite_creds, compression=None