diff --git a/src/mcp/client/session_group.py b/src/mcp/client/session_group.py
index 700b5417f..6657ccee6 100644
--- a/src/mcp/client/session_group.py
+++ b/src/mcp/client/session_group.py
@@ -16,7 +16,8 @@
 from typing import Any, TypeAlias
 
 import anyio
-from pydantic import BaseModel
+import httpx
+from pydantic import BaseModel, ConfigDict
 from typing_extensions import Self
 
 import mcp
@@ -30,6 +31,8 @@
 class SseServerParameters(BaseModel):
     """Parameters for intializing a sse_client."""
 
+    model_config = ConfigDict(arbitrary_types_allowed=True)
+
     # The endpoint URL.
     url: str
 
@@ -42,10 +45,15 @@ class SseServerParameters(BaseModel):
     # Timeout for SSE read operations.
     sse_read_timeout: float = 60 * 5
 
+    # Optional HTTPX authentication handler.
+    auth: httpx.Auth | None = None
+
 
 class StreamableHttpParameters(BaseModel):
     """Parameters for intializing a streamablehttp_client."""
 
+    model_config = ConfigDict(arbitrary_types_allowed=True)
+
     # The endpoint URL.
     url: str
 
@@ -61,6 +69,9 @@ class StreamableHttpParameters(BaseModel):
     # Close the client session when the transport closes.
     terminate_on_close: bool = True
 
+    # Optional HTTPX authentication handler.
+    auth: httpx.Auth | None = None
+
 
 ServerParameters: TypeAlias = StdioServerParameters | SseServerParameters | StreamableHttpParameters
 
diff --git a/src/mcp/client/sse.py b/src/mcp/client/sse.py
index 0c05c6def..61391cb4e 100644
--- a/src/mcp/client/sse.py
+++ b/src/mcp/client/sse.py
@@ -40,6 +40,7 @@ async def sse_client(
         headers: Optional headers to include in requests.
         timeout: HTTP timeout for regular operations.
         sse_read_timeout: Timeout for SSE read operations.
+        httpx_client_factory: McpHttpClientFactory.
         auth: Optional HTTPX authentication handler.
     """
     read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
diff --git a/src/mcp/client/streamable_http.py b/src/mcp/client/streamable_http.py
index 39ac34d8a..cb324d29f 100644
--- a/src/mcp/client/streamable_http.py
+++ b/src/mcp/client/streamable_http.py
@@ -460,6 +460,15 @@ async def streamablehttp_client(
     `sse_read_timeout` determines how long (in seconds) the client will wait for a new
     event before disconnecting. All other HTTP operations are controlled by `timeout`.
 
+    Args:
+        url: The SSE endpoint URL.
+        headers: Optional headers to include in requests.
+        timeout: HTTP timeout for regular operations.
+        sse_read_timeout: Timeout for SSE read operations.
+        terminate_on_close: Terminate session when stream closes.
+        httpx_client_factory: McpHttpClientFactory.
+        auth: Optional HTTPX authentication handler.
+
     Yields:
         Tuple containing:
             - read_stream: Stream for reading messages from the server
diff --git a/tests/client/test_session_group.py b/tests/client/test_session_group.py
index 16a887e00..b20af318e 100644
--- a/tests/client/test_session_group.py
+++ b/tests/client/test_session_group.py
@@ -272,12 +272,12 @@ async def test_disconnect_non_existent_server(self):
                 SseServerParameters(url="http://test.com/sse", timeout=10),
                 "sse",
                 "mcp.client.session_group.sse_client",
-            ),  # url, headers, timeout, sse_read_timeout
+            ),  # url, headers, timeout, sse_read_timeout, auth
             (
                 StreamableHttpParameters(url="http://test.com/stream", terminate_on_close=False),
                 "streamablehttp",
                 "mcp.client.session_group.streamablehttp_client",
-            ),  # url, headers, timeout, sse_read_timeout, terminate_on_close
+            ),  # url, headers, timeout, sse_read_timeout, terminate_on_close, auth
         ],
     )
     async def test_establish_session_parameterized(