diff --git a/httpx/__init__.py b/httpx/__init__.py
index f61112f8b2..ace7c299d1 100644
--- a/httpx/__init__.py
+++ b/httpx/__init__.py
@@ -1,7 +1,7 @@
 from .__version__ import __description__, __title__, __version__
 from ._api import delete, get, head, options, patch, post, put, request, stream
 from ._auth import Auth, BasicAuth, DigestAuth, NetRCAuth
-from ._client import USE_CLIENT_DEFAULT, AsyncClient, Client
+from ._client import USE_CLIENT_DEFAULT, AsyncClient, Client, UseClientDefault
 from ._config import Limits, Proxy, Timeout, create_ssl_context
 from ._content import ByteStream
 from ._exceptions import (
@@ -125,6 +125,7 @@ def main() -> None:  # type: ignore
     "TransportError",
     "UnsupportedProtocol",
     "URL",
+    "UseClientDefault",
     "USE_CLIENT_DEFAULT",
     "WriteError",
     "WriteTimeout",