fix(mcp): explain missing public client dependencies

litellm/experimental_mcp_client/Readme.md

@@ -2,6 +2,17 @@
 
 LiteLLM MCP Client allows you to use MCP tools with LiteLLM
 
+Install the optional dependencies with `pip install 'litellm[mcp]'`, then use the existing public imports:
+
+```python
+from litellm.experimental_mcp_client import call_openai_tool, load_mcp_tools
+from litellm.experimental_mcp_client.client import MCPClient
+
+client = MCPClient(server_url="https://mcp.example.com/mcp")
+```
+
+Core `import litellm` works without the MCP extra. Importing the experimental MCP client without its MCP or HTTPX2 dependency raises an error with this installation command
+
 ## MCP Python SDK compatibility
 
 The `mcp` and `proxy` extras require MCP Python SDK 2.2 or newer within the 2.x release line. Installing core LiteLLM without these extras does not require MCP
@@ -16,6 +27,12 @@ The shared unit-test workflow runs the MCP integration suite once, with SDK2 in
 
 See the official [SDK migration guide](https://py.sdk.modelcontextprotocol.io/migration/) for Python API changes
 
+## Custom HTTP clients and authentication
+
+MCP HTTP and SSE transports now use `httpx2`. Custom authentication passed through `aws_auth` or `resolved_auth` must implement `httpx2.Auth`. Integrations that override the client's HTTP client factory or customize its event hooks must use `httpx2.AsyncClient`, request, response, timeout and transport types
+
+HTTPX1 clients, auth objects and hooks are not adapted by a compatibility shim. Migrate those integrations to HTTPX2 before upgrading. Ordinary `MCPClient` construction and LiteLLM's existing helper imports remain supported; this does not restore SDK1 Python imports or camelCase SDK model attributes in the shared Python environment
+
 ## HTTP redirects
 
 For streamable HTTP POST requests, the MCP SDK follows method-preserving redirects such as HTTP 307/308 within the configured endpoint's origin. Redirects to another path on the same scheme, host and port work. The SDK also permits an HTTP-to-HTTPS upgrade on the same host using the default ports

litellm/experimental_mcp_client/__init__.py

@@ -1,3 +1,8 @@
-from .tools import call_openai_tool, load_mcp_tools
+try:
+    from .tools import call_openai_tool, load_mcp_tools
+except ModuleNotFoundError as exc:
+    if exc.name not in ("mcp", "httpx2"):
+        raise
+    raise ImportError("MCP client dependencies are missing. Install them with: pip install 'litellm[mcp]'") from exc
 
 __all__ = ["call_openai_tool", "load_mcp_tools"]

tests/base_sdk_tests/check_base_sdk_install.py

@@ -50,6 +50,17 @@ def check_completion() -> str:
     return "mock completion round-trips"
 
 
+def check_mcp_install_guidance() -> str:
+    try:
+        import litellm.experimental_mcp_client
+    except ImportError as error:
+        _require("pip install 'litellm[mcp]'" in str(error), f"missing MCP installation guidance: {error}")
+        _require(isinstance(error.__cause__, ModuleNotFoundError), "original missing-dependency cause was lost")
+        _require(error.__cause__.name == "mcp", f"unexpected missing dependency: {error.__cause__}")
+        return "optional MCP client explains how to install litellm[mcp]"
+    raise AssertionError("MCP client imported without the MCP extra")
+
+
 def check_embedding() -> str:
     import litellm
 
@@ -109,6 +120,7 @@ def check_bedrock_credential_resolution() -> str:
 CHECKS: tuple[tuple[str, Callable[[], str]], ...] = (
     ("environment is base-only", check_environment_is_base_only),
     ("import litellm", check_import),
+    ("optional MCP installation guidance", check_mcp_install_guidance),
     ("chat completion", check_completion),
     ("embedding", check_embedding),
     ("bundled model metadata", check_bundled_model_metadata),

tests/test_litellm/experimental_mcp_client/test_mcp_client.py

@@ -1,10 +1,12 @@
 import asyncio
 import base64
+import importlib
 import json
 import os
 import sys
 from collections.abc import AsyncIterator
 from pathlib import Path
+from types import ModuleType
 from typing import Final
 from unittest.mock import AsyncMock, MagicMock, Mock, patch
 
@@ -2160,3 +2162,38 @@ async def test_404_before_session_initialization_preserves_method_not_found() ->
             )
     assert caught.value.error.code == METHOD_NOT_FOUND
     assert caught.value.error.message == "Not Found"
+
+
+@pytest.mark.parametrize("missing_module", ("mcp", "httpx2", "mcp.types", "openai.types.chat"))
+def test_public_mcp_import_missing_dependency(missing_module: str) -> None:
+    with patch.dict(sys.modules):
+        for name in tuple(sys.modules):
+            if name.startswith(("litellm.experimental_mcp_client", "mcp.", "mcp_types.")) or name == "mcp":
+                del sys.modules[name]
+        with patch.dict(sys.modules, {missing_module: None}):
+            with pytest.raises(ImportError) as caught:
+                importlib.import_module("litellm.experimental_mcp_client.client")
+
+    if missing_module in ("mcp", "httpx2"):
+        assert "pip install 'litellm[mcp]'" in str(caught.value)
+        assert isinstance(caught.value.__cause__, ModuleNotFoundError)
+        assert caught.value.__cause__.name == missing_module
+    else:
+        assert isinstance(caught.value, ModuleNotFoundError)
+        assert caught.value.name == missing_module
+        assert caught.value.__cause__ is None
+        assert "litellm[mcp]" not in str(caught.value)
+
+
+def test_public_mcp_import_preserves_incompatible_sdk_error() -> None:
+    with patch.dict(sys.modules):
+        for name in tuple(sys.modules):
+            if name.startswith("litellm.experimental_mcp_client"):
+                del sys.modules[name]
+        with patch.dict(sys.modules, {"mcp": ModuleType("mcp")}):
+            with pytest.raises(ImportError, match="cannot import name 'ClientSession'") as caught:
+                importlib.import_module("litellm.experimental_mcp_client.client")
+
+    assert not isinstance(caught.value, ModuleNotFoundError)
+    assert caught.value.__cause__ is None
+    assert "litellm[mcp]" not in str(caught.value)