diff --git a/src/mcp/client/session_group.py b/src/mcp/client/session_group.py
index 700b5417f..d402ee082 100644
--- a/src/mcp/client/session_group.py
+++ b/src/mcp/client/session_group.py
@@ -13,7 +13,7 @@
 from collections.abc import Callable
 from datetime import timedelta
 from types import TracebackType
-from typing import Any, TypeAlias
+from typing import Any, Literal, TypeAlias
 
 import anyio
 from pydantic import BaseModel
@@ -30,6 +30,9 @@
 class SseServerParameters(BaseModel):
     """Parameters for intializing a sse_client."""
 
+    # The type of server connection.
+    type: Literal["sse"] = "sse"
+
     # The endpoint URL.
     url: str
 
@@ -46,6 +49,9 @@ class SseServerParameters(BaseModel):
 class StreamableHttpParameters(BaseModel):
     """Parameters for intializing a streamablehttp_client."""
 
+    # The type of server connection.
+    type: Literal["streamable_http"] = "streamable_http"
+
     # The endpoint URL.
     url: str
 
diff --git a/src/mcp/client/stdio/__init__.py b/src/mcp/client/stdio/__init__.py
index 50bceddec..804c2ec2f 100644
--- a/src/mcp/client/stdio/__init__.py
+++ b/src/mcp/client/stdio/__init__.py
@@ -69,6 +69,9 @@ def get_default_environment() -> dict[str, str]:
 
 
 class StdioServerParameters(BaseModel):
+    type: Literal["stdio"] = "stdio"
+    """The type of server connection."""
+
     command: str
     """The executable to run to start the server."""