diff --git a/datastore/google/cloud/datastore/_gax.py b/datastore/google/cloud/datastore/_gax.py
index b29ce874f298..58500301c950 100644
--- a/datastore/google/cloud/datastore/_gax.py
+++ b/datastore/google/cloud/datastore/_gax.py
@@ -17,15 +17,24 @@
 
 import contextlib
 
+from google.cloud.proto.datastore.v1 import datastore_pb2_grpc
+from google.gax.utils import metrics
 from grpc import StatusCode
 
 from google.cloud._helpers import make_insecure_stub
 from google.cloud._helpers import make_secure_stub
 from google.cloud import exceptions
 
-from google.cloud.proto.datastore.v1 import datastore_pb2_grpc
+from google.cloud.datastore import __version__
 
 
+_METRICS_HEADERS = (
+    ('gccl', __version__),
+)
+_HEADER_STR = metrics.stringify(metrics.fill(_METRICS_HEADERS))
+_GRPC_EXTRA_OPTIONS = (
+    ('x-goog-api-client', _HEADER_STR),
+)
 _GRPC_ERROR_MAPPING = {
     StatusCode.UNKNOWN: exceptions.InternalServerError,
     StatusCode.INVALID_ARGUMENT: exceptions.BadRequest,
@@ -85,10 +94,10 @@ class _DatastoreAPIOverGRPC(object):
 
     def __init__(self, connection, secure):
         if secure:
-            self._stub = make_secure_stub(connection.credentials,
-                                          connection.USER_AGENT,
-                                          datastore_pb2_grpc.DatastoreStub,
-                                          connection.host)
+            self._stub = make_secure_stub(
+                connection.credentials, connection.USER_AGENT,
+                datastore_pb2_grpc.DatastoreStub, connection.host,
+                extra_options=_GRPC_EXTRA_OPTIONS)
         else:
             self._stub = make_insecure_stub(datastore_pb2_grpc.DatastoreStub,
                                             connection.host)
diff --git a/datastore/setup.py b/datastore/setup.py
index 170692218b4f..625415c65ddb 100644
--- a/datastore/setup.py
+++ b/datastore/setup.py
@@ -51,7 +51,7 @@
 
 REQUIREMENTS = [
     'google-cloud-core >= 0.23.1, < 0.24dev',
-    'grpcio >= 1.0.2, < 2.0dev',
+    'google-gax>=0.15.7, <0.16dev',
     'gapic-google-cloud-datastore-v1 >= 0.15.0, < 0.16dev',
 ]
 
diff --git a/datastore/unit_tests/test__gax.py b/datastore/unit_tests/test__gax.py
index e0fc912e0081..419c85cc9fdc 100644
--- a/datastore/unit_tests/test__gax.py
+++ b/datastore/unit_tests/test__gax.py
@@ -97,7 +97,7 @@ def _get_target_class():
 
         return _DatastoreAPIOverGRPC
 
-    def _make_one(self, stub, connection=None, secure=True, mock_args=None):
+    def _make_one(self, stub, connection=None, secure=True):
         if connection is None:
             connection = mock.Mock(
                 credentials=object(),
@@ -106,27 +106,21 @@ def _make_one(self, stub, connection=None, secure=True, mock_args=None):
                 spec=['credentials', 'host', 'USER_AGENT'],
             )
 
-        if mock_args is None:
-            mock_args = []
-
-        def mock_make_stub(*args):
-            mock_args.append(args)
-            return stub
-
         if secure:
             patch = mock.patch(
                 'google.cloud.datastore._gax.make_secure_stub',
-                new=mock_make_stub)
+                return_value=stub)
         else:
             patch = mock.patch(
                 'google.cloud.datastore._gax.make_insecure_stub',
-                new=mock_make_stub)
+                return_value=stub)
 
-        with patch:
-            return self._get_target_class()(connection, secure)
+        with patch as make_stub_mock:
+            api_obj = self._get_target_class()(connection, secure)
+            return api_obj, make_stub_mock
 
     def test_constructor(self):
-        from google.cloud.proto.datastore.v1 import datastore_pb2_grpc
+        import google.cloud.datastore._gax as MUT
 
         conn = mock.Mock(
             credentials=object(),
@@ -136,17 +130,17 @@ def test_constructor(self):
         )
 
         stub = _GRPCStub()
-        mock_args = []
-        datastore_api = self._make_one(stub, connection=conn,
-                                       mock_args=mock_args)
-        self.assertIs(datastore_api._stub, stub)
+        datastore_api, make_stub_mock = self._make_one(
+            stub, connection=conn)
 
-        self.assertEqual(mock_args, [(
+        self.assertIs(datastore_api._stub, stub)
+        make_stub_mock.assert_called_once_with(
             conn.credentials,
             conn.USER_AGENT,
-            datastore_pb2_grpc.DatastoreStub,
+            MUT.datastore_pb2_grpc.DatastoreStub,
             conn.host,
-        )])
+            extra_options=MUT._GRPC_EXTRA_OPTIONS,
+        )
 
     def test_constructor_insecure(self):
         from google.cloud.proto.datastore.v1 import datastore_pb2_grpc
@@ -158,21 +152,19 @@ def test_constructor_insecure(self):
         )
 
         stub = _GRPCStub()
-        mock_args = []
-        datastore_api = self._make_one(stub, connection=conn,
-                                       secure=False,
-                                       mock_args=mock_args)
-        self.assertIs(datastore_api._stub, stub)
+        datastore_api, make_stub_mock = self._make_one(
+            stub, connection=conn, secure=False)
 
-        self.assertEqual(mock_args, [(
+        self.assertIs(datastore_api._stub, stub)
+        make_stub_mock.assert_called_once_with(
             datastore_pb2_grpc.DatastoreStub,
             conn.host,
-        )])
+        )
 
     def test_lookup(self):
         return_val = object()
         stub = _GRPCStub(return_val)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'
@@ -185,7 +177,7 @@ def test_lookup(self):
     def test_run_query(self):
         return_val = object()
         stub = _GRPCStub(return_val)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'
@@ -197,7 +189,7 @@ def test_run_query(self):
 
     def _run_query_failure_helper(self, exc, err_class):
         stub = _GRPCStub(side_effect=exc)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'
@@ -225,7 +217,7 @@ def test_run_query_invalid_argument(self):
     def test_begin_transaction(self):
         return_val = object()
         stub = _GRPCStub(return_val)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'
@@ -239,7 +231,7 @@ def test_begin_transaction(self):
     def test_commit_success(self):
         return_val = object()
         stub = _GRPCStub(return_val)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'
@@ -252,7 +244,7 @@ def test_commit_success(self):
     def test_rollback(self):
         return_val = object()
         stub = _GRPCStub(return_val)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'
@@ -265,7 +257,7 @@ def test_rollback(self):
     def test_allocate_ids(self):
         return_val = object()
         stub = _GRPCStub(return_val)
-        datastore_api = self._make_one(stub=stub)
+        datastore_api, _ = self._make_one(stub=stub)
 
         request_pb = mock.Mock(project_id=None, spec=['project_id'])
         project = 'PROJECT'