fix(mcp): add litellm[mcp] extra and actionable error when streamable_http_client is missing

The MCP client's HTTP transport needs mcp>=1.24.0 for streamable_http_client,
but a base litellm install declares no mcp constraint and no extra existed to
pin one, so environments carrying an older mcp fail at connect time with
'streamable_http_client is not available. Please install mcp with HTTP
support.', which names no version floor and no installable remedy.

Add a litellm[mcp] extra matching the proxy extra's mcp>=1.28.1,<2.0 and
replace the vague ImportError with one naming the required floor, the
installed mcp version, and the pip commands that fix it.

litellm/experimental_mcp_client/client.py

@@ -7,6 +7,7 @@ import base64
 import os
 from collections.abc import Awaitable, Callable, Generator
 from datetime import timedelta
+from importlib import metadata
 from typing import Any, Final, TypeVar
 
 import httpx
@@ -21,6 +22,18 @@ try:
     streamable_http_client = getattr(streamable_http_module, "streamable_http_client", None)
 except ImportError:
     pass
+
+MCP_STREAMABLE_HTTP_REQUIREMENT: Final = "mcp>=1.28.1"
+
+
+def missing_streamable_http_client_error() -> ImportError:
+    return ImportError(
+        f"MCP streamable HTTP transport requires {MCP_STREAMABLE_HTTP_REQUIREMENT}, but the installed "
+        f"mcp {metadata.version('mcp')} does not provide streamable_http_client. "
+        "Fix with: pip install 'litellm[mcp]' (or upgrade mcp directly: pip install -U mcp)"
+    )
+
+
 from mcp.types import CallToolRequestParams as MCPCallToolRequestParams
 from mcp.types import CallToolResult as MCPCallToolResult
 from mcp.types import (
@@ -323,7 +336,7 @@ class MCPClient:
             )
         # HTTP transport (default)
         if streamable_http_client is None:
-            raise ImportError("streamable_http_client is not available. Please install mcp with HTTP support.")
+            raise missing_streamable_http_client_error()
         headers = self._get_auth_headers()
         httpx_client_factory = self._create_httpx_client_factory()
         verbose_logger.debug("litellm headers for streamable_http_client: %s", headers)

pyproject.toml

@@ -106,6 +106,7 @@ utils = [
     "numpydoc>=1.8.0,<2.0",
 ]
 caching = ["diskcache>=5.6.3,<6.0"]
+mcp = ["mcp>=1.28.1,<2.0"]
 # SAML SSO for the admin UI. python3-saml pulls in xmlsec/lxml, whose wheels
 # bundle the native libxmlsec1/libxml2 libraries, so no system packages are
 # required. Kept out of the base `proxy` extra so it stays optional.

tests/test_litellm/experimental_mcp_client/test_mcp_client.py

@@ -2,6 +2,8 @@ import asyncio
 import base64
 import os
 import sys
+from importlib import metadata
+from pathlib import Path
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import anyio
@@ -24,9 +26,11 @@ from mcp.types import (
 
 import litellm.experimental_mcp_client.client as mcp_client_module
 from litellm.experimental_mcp_client.client import (
+    MCP_STREAMABLE_HTTP_REQUIREMENT,
     MCPClient,
     _as_read_timeout,
     _first_non_cancelled_cause,
+    missing_streamable_http_client_error,
     strip_auth_scheme,
 )
 from litellm.proxy._experimental.mcp_server.faults.list_outcomes import (
@@ -1047,3 +1051,42 @@ def test_openapi_byok_auth_header_emits_exactly_one_scheme(auth_type, auth_value
 
     assert server.is_byok is False
     assert _format_byok_openapi_auth_header(server, auth_value) == expected
+
+
+def test_missing_streamable_http_client_error_names_requirement_and_remedy():
+    message = str(missing_streamable_http_client_error())
+
+    assert MCP_STREAMABLE_HTTP_REQUIREMENT in message
+    assert "pip install 'litellm[mcp]'" in message
+    assert metadata.version("mcp") in message
+
+
+@pytest.mark.asyncio
+async def test_http_transport_without_streamable_http_client_raises_actionable_import_error():
+    client = MCPClient(
+        server_url="https://mcp-server.example.com",
+        transport_type=MCPTransport.http,
+    )
+
+    with patch.object(mcp_client_module, "streamable_http_client", None):  # test-quality-ok: simulates mcp<1.24.0 whose module lacks this import-time symbol; no HTTP boundary exists before the raise
+        with pytest.raises(ImportError, match=r"pip install 'litellm\[mcp\]'"):
+            await client.list_tools(raise_on_error=True)
+
+
+def test_mcp_extra_matches_proxy_extra_and_supports_streamable_http():
+    tomllib = pytest.importorskip("tomllib")
+    from packaging.requirements import Requirement
+
+    pyproject_path = Path(__file__).parents[3] / "pyproject.toml"
+    with pyproject_path.open("rb") as f:
+        extras = tomllib.load(f)["project"]["optional-dependencies"]
+
+    mcp_extra = extras["mcp"]
+    assert len(mcp_extra) == 1
+
+    proxy_mcp_requirements = [req for req in extras["proxy"] if Requirement(req).name == "mcp"]
+    assert mcp_extra == proxy_mcp_requirements
+
+    specifier = Requirement(mcp_extra[0]).specifier
+    assert not specifier.contains("1.23.0")
+    assert specifier.contains("1.28.1")

uv.lock

@@ -10,7 +10,7 @@ resolution-markers = [
 ]
 
 [options]
-exclude-newer = "2026-08-23T02:27:57.028643Z"
+exclude-newer = "2026-08-23T20:15:58.934396Z"
 exclude-newer-span = "P3D"
 
 [manifest]
@@ -4315,6 +4315,9 @@ google = [
 grpc = [
     { name = "grpcio" },
 ]
+mcp = [
+    { name = "mcp" },
+]
 mlflow = [
     { name = "mlflow" },
 ]
@@ -4526,6 +4529,7 @@ requires-dist = [
     { name = "litellm-proxy-extras", marker = "extra == 'proxy'", editable = "litellm-proxy-extras" },
     { name = "llm-sandbox", marker = "extra == 'proxy-runtime'", specifier = ">=0.3.39,<1.0" },
     { name = "mangum", marker = "extra == 'proxy-runtime'", specifier = ">=0.17.0,<1.0" },
+    { name = "mcp", marker = "extra == 'mcp'", specifier = ">=1.28.1,<2.0" },
     { name = "mcp", marker = "extra == 'proxy'", specifier = ">=1.28.1,<2.0" },
     { name = "mlflow", marker = "extra == 'mlflow'", specifier = ">=3.11.1,<4.0" },
     { name = "numpy", marker = "extra == 'stt-nvidia-riva'", specifier = ">=1.26.0" },
@@ -4569,7 +4573,7 @@ requires-dist = [
     { name = "uvloop", marker = "sys_platform != 'win32' and extra == 'proxy'", specifier = ">=0.21.0,<1.0" },
     { name = "websockets", marker = "extra == 'proxy'", specifier = ">=15.0.1,<16.0" },
 ]
-provides-extras = ["proxy", "cli", "extra-proxy", "utils", "caching", "saml", "semantic-router", "mlflow", "grpc", "stt-nvidia-riva", "google", "bedrock-realtime", "proxy-runtime"]
+provides-extras = ["proxy", "cli", "extra-proxy", "utils", "caching", "mcp", "saml", "semantic-router", "mlflow", "grpc", "stt-nvidia-riva", "google", "bedrock-realtime", "proxy-runtime"]
 
 [package.metadata.requires-dev]
 ci = [