Support custom client info throughout client APIs (#474)

Co-authored-by: Claude <noreply@anthropic.com>

src/mcp/client/__main__.py

@@ -38,9 +38,13 @@ async def message_handler(
 async def run_session(
     read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception],
     write_stream: MemoryObjectSendStream[JSONRPCMessage],
+    client_info: types.Implementation | None = None,
 ):
     async with ClientSession(
-        read_stream, write_stream, message_handler=message_handler
+        read_stream,
+        write_stream,
+        message_handler=message_handler,
+        client_info=client_info,
     ) as session:
         logger.info("Initializing session")
         await session.initialize()

src/mcp/client/session.py

@@ -10,6 +10,8 @@ from mcp.shared.context import RequestContext
 from mcp.shared.session import BaseSession, RequestResponder
 from mcp.shared.version import SUPPORTED_PROTOCOL_VERSIONS
 
+DEFAULT_CLIENT_INFO = types.Implementation(name="mcp", version="0.1.0")
+
 
 class SamplingFnT(Protocol):
     async def __call__(
@@ -97,6 +99,7 @@ class ClientSession(
         list_roots_callback: ListRootsFnT | None = None,
         logging_callback: LoggingFnT | None = None,
         message_handler: MessageHandlerFnT | None = None,
+        client_info: types.Implementation | None = None,
     ) -> None:
         super().__init__(
             read_stream,
@@ -105,6 +108,7 @@ class ClientSession(
             types.ServerNotification,
             read_timeout_seconds=read_timeout_seconds,
         )
+        self._client_info = client_info or DEFAULT_CLIENT_INFO
         self._sampling_callback = sampling_callback or _default_sampling_callback
         self._list_roots_callback = list_roots_callback or _default_list_roots_callback
         self._logging_callback = logging_callback or _default_logging_callback
@@ -130,7 +134,7 @@ class ClientSession(
                             experimental=None,
                             roots=roots,
                         ),
-                        clientInfo=types.Implementation(name="mcp", version="0.1.0"),
+                        clientInfo=self._client_info,
                     ),
                 )
             ),

src/mcp/shared/memory.py

@@ -10,6 +10,7 @@ from typing import Any
 import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 
+import mcp.types as types
 from mcp.client.session import (
     ClientSession,
     ListRootsFnT,
@@ -65,6 +66,7 @@ async def create_connected_server_and_client_session(
     list_roots_callback: ListRootsFnT | None = None,
     logging_callback: LoggingFnT | None = None,
     message_handler: MessageHandlerFnT | None = None,
+    client_info: types.Implementation | None = None,
     raise_exceptions: bool = False,
 ) -> AsyncGenerator[ClientSession, None]:
     """Creates a ClientSession that is connected to a running MCP server."""
@@ -95,6 +97,7 @@ async def create_connected_server_and_client_session(
                     list_roots_callback=list_roots_callback,
                     logging_callback=logging_callback,
                     message_handler=message_handler,
+                    client_info=client_info,
                 ) as client_session:
                     await client_session.initialize()
                     yield client_session