diff --git a/google/genai/_api_client.py b/google/genai/_api_client.py
index 4d90ba86e..07b821f03 100644
--- a/google/genai/_api_client.py
+++ b/google/genai/_api_client.py
@@ -30,6 +30,7 @@
 import math
 import os
 import random
+import socket
 import ssl
 import sys
 import threading
@@ -557,12 +558,39 @@ def retry_args(options: Optional[HttpRetryOptions]) -> _common.StringDict:
   }
 
 
+def _default_socket_options() -> list[tuple[int, int, int]]:
+  """Returns socket options that enable TCP keepalive on connections.
+
+  Long-running calls can stay silent on the wire for longer than the idle
+  timeout of NAT gateways and stateful firewalls on the egress path. Without
+  keepalive probes such connections are dropped silently and the response
+  read hangs forever (https://github.com/googleapis/python-genai/issues/2705).
+  """
+  options = [(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)]
+  # Start sending keepalive probes after 60 seconds of idleness, well below
+  # common NAT idle timeouts. The option name is platform dependent: Linux
+  # and Windows expose TCP_KEEPIDLE; macOS uses TCP_KEEPALIVE.
+  if hasattr(socket, 'TCP_KEEPIDLE'):
+    options.append((socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 60))
+  elif hasattr(socket, 'TCP_KEEPALIVE'):
+    options.append((socket.IPPROTO_TCP, socket.TCP_KEEPALIVE, 60))
+  if hasattr(socket, 'TCP_KEEPINTVL'):
+    options.append((socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, 60))
+  if hasattr(socket, 'TCP_KEEPCNT'):
+    options.append((socket.IPPROTO_TCP, socket.TCP_KEEPCNT, 5))
+  return options
+
+
 class SyncHttpxClient(httpx.Client):
   """Sync httpx client."""
 
   def __init__(self, **kwargs: Any) -> None:
     """Initializes the httpx client."""
     kwargs.setdefault('follow_redirects', True)
+    if 'transport' not in kwargs and 'mounts' not in kwargs:
+      kwargs['transport'] = httpx.HTTPTransport(
+          socket_options=_default_socket_options()
+      )
     super().__init__(**kwargs)
 
   def __del__(self) -> None:
@@ -584,6 +612,10 @@ class AsyncHttpxClient(httpx.AsyncClient):
   def __init__(self, **kwargs: Any) -> None:
     """Initializes the httpx client."""
     kwargs.setdefault('follow_redirects', True)
+    if 'transport' not in kwargs and 'mounts' not in kwargs:
+      kwargs['transport'] = httpx.AsyncHTTPTransport(
+          socket_options=_default_socket_options()
+      )
     super().__init__(**kwargs)
 
   def __del__(self) -> None:
diff --git a/google/genai/tests/client/test_socket_options.py b/google/genai/tests/client/test_socket_options.py
new file mode 100644
index 000000000..d1ff66eed
--- /dev/null
+++ b/google/genai/tests/client/test_socket_options.py
@@ -0,0 +1,67 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""Tests for TCP keepalive on the default httpx transports.
+
+Regression tests for https://github.com/googleapis/python-genai/issues/2705:
+without TCP keepalive, long-running calls that stay silent on the wire are
+evicted by NAT gateways and stateful firewalls, hanging the read forever.
+"""
+
+import socket
+
+import httpx
+
+from ... import _api_client as api_client
+
+
+def test_default_socket_options_enable_keepalive():
+  options = api_client._default_socket_options()
+  assert (socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1) in options
+  # At least one platform-specific keepalive tuning option must be present so
+  # probes start before typical NAT idle timeouts.
+  assert len(options) > 1
+
+
+def test_sync_client_gets_keepalive_transport_by_default():
+  client = api_client.SyncHttpxClient()
+  assert isinstance(client._transport, httpx.HTTPTransport)
+  assert (
+      socket.SOL_SOCKET,
+      socket.SO_KEEPALIVE,
+      1,
+  ) in client._transport._pool._socket_options
+
+
+def test_async_client_gets_keepalive_transport_by_default():
+  client = api_client.AsyncHttpxClient()
+  assert isinstance(client._transport, httpx.AsyncHTTPTransport)
+  assert (
+      socket.SOL_SOCKET,
+      socket.SO_KEEPALIVE,
+      1,
+  ) in client._transport._pool._socket_options
+
+
+def test_sync_client_preserves_user_transport():
+  transport = httpx.MockTransport(lambda request: httpx.Response(200))
+  client = api_client.SyncHttpxClient(transport=transport)
+  assert client._transport is transport
+
+
+def test_async_client_preserves_user_transport():
+  transport = httpx.MockTransport(lambda request: httpx.Response(200))
+  client = api_client.AsyncHttpxClient(transport=transport)
+  assert client._transport is transport