diff --git a/pubsub/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py b/pubsub/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py
index bc3059cb69af..f3798c05610e 100644
--- a/pubsub/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py
+++ b/pubsub/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py
@@ -51,13 +51,6 @@
 _RESUME_THRESHOLD = 0.8
 """The load threshold below which to resume the incoming message stream."""
 
-_DEFAULT_STREAM_ACK_DEADLINE = 60
-"""The default message acknowledge deadline in seconds for incoming message stream.
-
-This default deadline is dynamically modified for the messages that are added
-to the lease management.
-"""
-
 
 def _maybe_wrap_exception(exception):
     """Wraps a gRPC exception class, if needed."""
@@ -412,17 +405,7 @@ def open(self, callback, on_callback_error):
         )
 
         # Create the RPC
-
-        # We must use a fixed value for the ACK deadline, as we cannot read it
-        # from the subscription. The latter would require `pubsub.subscriptions.get`
-        # permission, which is not granted to the default subscriber role
-        # `roles/pubsub.subscriber`.
-        # See also https://github.com/googleapis/google-cloud-python/issues/9339
-        #
-        # When dynamic lease management is enabled for the "on hold" messages,
-        # the default stream ACK deadline should again be set based on the
-        # historic ACK timing data, i.e. `self.ack_histogram.percentile(99)`.
-        stream_ack_deadline_seconds = _DEFAULT_STREAM_ACK_DEADLINE
+        stream_ack_deadline_seconds = self.ack_histogram.percentile(99)
 
         get_initial_request = functools.partial(
             self._get_initial_request, stream_ack_deadline_seconds
diff --git a/pubsub/tests/system.py b/pubsub/tests/system.py
index fd7473e1e53b..59e5e3fe83a4 100644
--- a/pubsub/tests/system.py
+++ b/pubsub/tests/system.py
@@ -382,10 +382,6 @@ class CallbackError(Exception):
         with pytest.raises(CallbackError):
             future.result(timeout=30)
 
-    @pytest.mark.xfail(
-        reason="The default stream ACK deadline is static and received messages "
-        "exceeding FlowControl.max_messages are currently not lease managed."
-    )
     def test_streaming_pull_ack_deadline(
         self, publisher, subscriber, project, topic_path, subscription_path, cleanup
     ):
@@ -400,7 +396,7 @@ def test_streaming_pull_ack_deadline(
         # Subscribe to the topic. This must happen before the messages
         # are published.
         subscriber.create_subscription(
-            subscription_path, topic_path, ack_deadline_seconds=240
+            subscription_path, topic_path, ack_deadline_seconds=45
         )
 
         # publish some messages and wait for completion
@@ -408,7 +404,7 @@ def test_streaming_pull_ack_deadline(
 
         # subscribe to the topic
         callback = StreamingPullCallback(
-            processing_time=70,  # more than the default stream ACK deadline (60s)
+            processing_time=13,  # more than the default stream ACK deadline (10s)
             resolve_at_msg_count=3,  # one more than the published messages count
         )
         flow_control = types.FlowControl(max_messages=1)
@@ -416,13 +412,13 @@ def test_streaming_pull_ack_deadline(
             subscription_path, callback, flow_control=flow_control
         )
 
-        # We expect to process the first two messages in 2 * 70 seconds, and
+        # We expect to process the first two messages in 2 * 13 seconds, and
         # any duplicate message that is re-sent by the backend in additional
-        # 70 seconds, totalling 210 seconds (+ overhead) --> if there have been
-        # no duplicates in 240 seconds, we can reasonably assume that there
+        # 13 seconds, totalling 39 seconds (+ overhead) --> if there have been
+        # no duplicates in 60 seconds, we can reasonably assume that there
         # won't be any.
         try:
-            callback.done_future.result(timeout=240)
+            callback.done_future.result(timeout=60)
         except exceptions.TimeoutError:
             # future timed out, because we received no excessive messages
             assert sorted(callback.seen_message_ids) == [1, 2]
diff --git a/pubsub/tests/unit/pubsub_v1/subscriber/test_streaming_pull_manager.py b/pubsub/tests/unit/pubsub_v1/subscriber/test_streaming_pull_manager.py
index 761ac073083c..1732ec6cd4b3 100644
--- a/pubsub/tests/unit/pubsub_v1/subscriber/test_streaming_pull_manager.py
+++ b/pubsub/tests/unit/pubsub_v1/subscriber/test_streaming_pull_manager.py
@@ -429,8 +429,6 @@ def test_heartbeat_inactive():
     "google.cloud.pubsub_v1.subscriber._protocol.heartbeater.Heartbeater", autospec=True
 )
 def test_open(heartbeater, dispatcher, leaser, background_consumer, resumable_bidi_rpc):
-    stream_ack_deadline = streaming_pull_manager._DEFAULT_STREAM_ACK_DEADLINE
-
     manager = make_manager()
 
     manager.open(mock.sentinel.callback, mock.sentinel.on_callback_error)
@@ -460,7 +458,7 @@ def test_open(heartbeater, dispatcher, leaser, background_consumer, resumable_bi
     )
     initial_request_arg = resumable_bidi_rpc.call_args.kwargs["initial_request"]
     assert initial_request_arg.func == manager._get_initial_request
-    assert initial_request_arg.args[0] == stream_ack_deadline
+    assert initial_request_arg.args[0] == 10  # the default stream ACK timeout
     assert not manager._client.api.get_subscription.called
 
     resumable_bidi_rpc.return_value.add_done_callback.assert_called_once_with(