c792df64d2 feat(mcp): support stateless and stateful clients via session-id routing (#26857)
* feat(mcp): support stateless and stateful clients via session-id routing

- Add session_manager_stateful (stateless=False) alongside stateless
- Route by mcp-session-id: has ID → stateful, initialize (no ID) → stateful, else → stateless
- Peek POST body to detect initialize for routing; replay via wrapped receive
- Handle stale session IDs for both managers
- Add test_mcp_routing_initialize_to_stateful_no_session_to_stateless
- Update test_valid_mcp_session_id_is_preserved, test_concurrent_initialize_session_managers

Made-with: Cursor

* fix(mcp): respect stateful routing and harden initialize detection

Ensure streamable MCP requests are dispatched via the computed target session manager, and guard initialize detection against non-object JSON bodies. Update stale-session test patches to target the stateful manager so routing assertions remain correct.

Made-with: Cursor

* test(mcp): patch stateless/stateful managers in concurrency init test

Update concurrent session-manager initialization test to patch session_manager_stateless and session_manager_stateful directly, matching initialize_session_managers() behavior and preventing NameError from undefined mocks.

Made-with: Cursor

* Fix tests

* Fix tests

* Fix MCP stateful routing edge cases

* Fix stateful MCP auth context refresh

* Fix MCP stateful session cleanup

* fix(mcp): bind stateful sessions to creator and reject hijacks

Stateful mcp-session-id was usable by any authenticated proxy caller. Track
the session creator's hashed API key (or user_id) when a new session is
issued and reject mismatched callers with 403 before _set_or_update_auth_context
overwrites the stored MCPAuthenticatedUser. Also formats nested with-statements
in test_mcp_stale_session.py and fixes a pre-existing AsyncMock mismatch in
test_stale_mcp_session_id_is_stripped.

* fix(mcp): serialize concurrent requests on same stateful session

Bugbot's 'Concurrent requests share context' finding: _update_auth_context
mutates the single MCPAuthenticatedUser stored per session in place on
every request, so two requests sharing one mcp-session-id can overwrite
each other's mcp_servers / auth headers / oauth state / client_ip while
in-flight callbacks are still reading the same object.

Owner-binding alone narrows this to same-principal racing, but the
in-place mutation race remains. Add a per-session asyncio.Lock around
handle_request so concurrent same-session requests run sequentially. The
lock is allocated on demand and torn down with the rest of the session
state on DELETE / idle expiry.

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* fix(mcp): include OAuth2 bearer in stateful session owner fingerprint

UserAPIKeyAuth() for OAuth2 passthrough has no api_key/user_id, so every
OAuth caller fingerprinted to "anonymous" and could hijack another OAuth
caller's mcp-session-id. Hash the upstream Authorization header into the
fingerprint as oauth:<sha256>.

* fix(mcp): don't hold stateful session lock for streaming GETs

The per-session lock wraps handle_request, so a long-lived GET (SSE
stream held open for the life of the session) would block every
subsequent POST on the same mcp-session-id. Only POST/DELETE mutate the
shared MCPAuthenticatedUser, so it's sufficient to serialize those —
GETs run lock-free and stream concurrently.

* fix(mcp): allow None user_api_key_auth in MCPAuthenticatedUser

The set_auth_context / _set_or_update_auth_context / _update_auth_context
helpers in server.py all accept Optional[UserAPIKeyAuth] and pass it
straight into MCPAuthenticatedUser, but the dataclass-style constructor
typed user_api_key_auth as required UserAPIKeyAuth. Mypy flagged this on
the stateful-routing branch:

  server.py:3227: error: Incompatible types in assignment (expression
    has type "UserAPIKeyAuth | None", variable has type "UserAPIKeyAuth")
  server.py:3255: error: Argument "user_api_key_auth" to
    "MCPAuthenticatedUser" has incompatible type "UserAPIKeyAuth | None";
    expected "UserAPIKeyAuth"

Widen the parameter type to Optional[UserAPIKeyAuth] to match the call
sites. Runtime behavior is unchanged.

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* style: replace with new alias

* fix(mcp): fall back to client_ip in stateful session owner fingerprint

Addresses Greptile review on PR #26857: when no API key, user_id, or
OAuth bearer is available (e.g. unauthenticated/passthrough callers),
the owner fingerprint collapsed to a single 'anonymous' value, allowing
two unrelated callers to drive each other's stateful MCP sessions.

Fold client IP into the fingerprint as a fallback identity signal so
distinct anonymous sources do not share an owner identity.

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Fix active stateful MCP session cleanup

* test(mcp): cancel leaked stateful auth-context cleanup task

initialize_session_managers() spawns a real asyncio.create_task running
_cleanup_expired_stateful_session_auth_contexts(). The
test_concurrent_initialize_session_managers test was saving and
restoring the session-manager context-manager globals but did not save,
cancel, or restore _stateful_auth_context_cleanup_task.

Because pyproject.toml sets asyncio_default_fixture_loop_scope=session,
the event loop is shared across tests in the same session, so the
leaked task kept running against module-level dicts for the rest of the
test run. Save and cancel the task in the finally block so the test
fully cleans up after itself.

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Fix stateful MCP session fingerprinting

* Hash MCP session user owner fingerprints

* Fix stale MCP session DELETE cleanup

* fix(mcp): harden owner fingerprint hashing for non-str api keys

_owner_fingerprint_for assumed api_key/user_id supported .encode();
MagicMock-based tests (and any non-str truthy values) crashed with
TypeError before routing. Only hash str/bytes secrets; fall through
otherwise so MCP routing and session tests behave correctly.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Fix MCP stateful cleanup loop resilience

* Fix stateful MCP initialize auth capture

* fix(mcp): drop orphan per-session lock when auth context absent

Defensive cleanup for _stateful_session_locks entries created on
sessions that never enter _stateful_session_auth_contexts. The
periodic cleanup loop only iterates auth_context_last_seen, so such
locks would otherwise live forever. Add a test that reproduces the
leak and verifies the request finalizer pops the lock.

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* chore(mcp): trim verbose comment on lock cleanup

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Fix stateful MCP delete failure tracking

* fix test

* fix(mcp): cap routing-peek body size to bound pre-dispatch memory

Authenticated clients that POST without an mcp-session-id forced the proxy
to buffer the entire request body before routing, since the peek loop
drained every body chunk to decide whether the JSON-RPC method was
'initialize'. Cap the peek at 4 KB (more than enough for an initialize
envelope) and let the remainder stream through wrapped_receive into the
downstream handler.

* test: replace dall-e-3 with gpt-image-1 in health check and router tests (#27813)

OpenAI returns 'The model dall-e-3 does not exist' for the test account,
breaking test_openai_img_gen_health_check and test_image_generation.
Switch to gpt-image-1, matching the existing TestOpenAIGPTImage1 pattern.

* fix(tests): drop dall-e-only test classes; route live image tests via gpt-image-1

Second wave of failures from the 2026-05-12 DALL-E shutdown:
- tests/image_gen_tests/test_image_edits.py::TestOpenAIImageEditDallE2
  and tests/image_gen_tests/test_image_generation.py::TestOpenAIDalle3
  are explicitly named for the deprecated models and can't pass; remove.
  gpt-image-1 coverage already exists in sibling classes.
- tests/local_testing/test_router.py image gen tests use dall-e-3 only
  as a routing example; swap to gpt-image-1.
- tests/local_testing/test_custom_callback_input.py image_generation
  success/failure paths swapped to gpt-image-1.

* Fix MCP initialize session active tracking

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* Fix MCP reinitialize session tracking

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* Fix MCP reinitialize auth context aliasing

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* Apply black formatting after merge

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Run owner-binding 403 before consuming POST body

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Harden MCP routing peek bound and stateful purge race

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Remove inadvertently committed Next.js build artifacts

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* Run owner check before stale MCP session cleanup

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* fix(mcp): reverse cleanup ordering to terminate transport before clearing owner

Reverses _purge_expired_stateful_session_auth_contexts so the transport
is popped from server_instances and terminated BEFORE owner/auth tracking
is cleared. The previous order left a window where _stateful_session_owners
was already empty but server_instances still served the session, so a
concurrent request would observe expected_owner is None and bypass the
owner-binding check. Addresses Greptile review on PR #26857.

Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>

* test(mcp): fully reset stateful session tracking in auth-context refresh test

Use _remove_stateful_session_tracking in teardown so the test no longer
leaks _stateful_session_auth_context_last_seen and _stateful_session_locks
between tests, matching the cleanup used by the sibling stateful tests.

* fix(mcp): cap concurrent stateful sessions per caller to bound memory

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Co-authored-by: Mateo Wang <mateo-berri@users.noreply.github.com>
Co-authored-by: Sameerlite <sameerlite@users.noreply.github.com>
Co-authored-by: yuneng-jiang <yuneng@berri.ai>
Co-authored-by: Yassin Kortam <yassin@berri.ai>
Co-authored-by: Claude Babysitter <claude@anthropic.com>
Co-authored-by: mateo-berri <mateo@berri.ai>
2026-05-29 20:30:36 -07:00
2025-11-01 12:58:39 -07:00
2026-05-16 18:31:43 -07:00
2024-02-15 12:54:13 -08:00
2026-05-18 16:27:44 -07:00
2026-05-18 16:27:44 -07:00
2026-03-31 13:13:18 -07:00
2026-05-28 18:49:04 -07:00

🚅 LiteLLM

LiteLLM AI Gateway

Open Source AI Gateway for 100+ LLMs. Self-hosted. Enterprise-ready. Call any LLM in OpenAI format.

Deploy to Render Deploy on Railway

LiteLLM Proxy Server (AI Gateway) | Hosted Proxy | Enterprise Tier | Website

PyPI Version GitHub Stars Y Combinator W23 Whatsapp Discord Slack CodSpeed

Group 7154 (1)

What is LiteLLM

LiteLLM is an open source AI Gateway that gives you a single, unified interface to call 100+ LLM providers — OpenAI, Anthropic, Gemini, Bedrock, Azure, and more — using the OpenAI format.

Use it as a Python SDK for direct library integration, or deploy the AI Gateway (Proxy Server) as a centralized service for your team or organization.

Jump to LiteLLM Proxy (LLM Gateway) Docs
Jump to Supported LLM Providers


Why LiteLLM

Managing LLM calls across providers gets complicated fast — different SDKs, auth patterns, request formats, and error types for every model. LiteLLM removes that friction:

  • Unified API — one interface for 100+ LLMs, no provider-specific SDK juggling
  • Drop-in OpenAI compatibility — swap providers without rewriting your code
  • Production-ready gateway — virtual keys, spend tracking, guardrails, load balancing, and an admin dashboard out of the box
  • 8ms P95 latency at 1k RPS (benchmarks)

OSS Adopters

Stripe image Google ADK Greptile OpenHands

Netflix

OpenAI Agents SDK

Features

LLMs - Call 100+ LLMs (Python SDK + AI Gateway)

All Supported Endpoints - /chat/completions, /responses, /embeddings, /images, /audio, /batches, /rerank, /a2a, /messages and more.

Python SDK

uv add litellm
from litellm import completion
import os

os.environ["OPENAI_API_KEY"] = "your-openai-key"
os.environ["ANTHROPIC_API_KEY"] = "your-anthropic-key"

# OpenAI
response = completion(model="openai/gpt-4o", messages=[{"role": "user", "content": "Hello!"}])

# Anthropic  
response = completion(model="anthropic/claude-sonnet-4-20250514", messages=[{"role": "user", "content": "Hello!"}])

AI Gateway (Proxy Server)

Getting Started - E2E Tutorial - Setup virtual keys, make your first request

uv tool install 'litellm[proxy]'
litellm --model gpt-4o
import openai

client = openai.OpenAI(api_key="anything", base_url="http://0.0.0.0:4000")
response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello!"}]
)

Docs: LLM Providers

Agents - Invoke A2A Agents (Python SDK + AI Gateway)

Supported Providers - LangGraph, Vertex AI Agent Engine, Azure AI Foundry, Bedrock AgentCore, Pydantic AI

Python SDK - A2A Protocol

from litellm.a2a_protocol import A2AClient
from a2a.types import SendMessageRequest, MessageSendParams
from uuid import uuid4

client = A2AClient(base_url="http://localhost:10001")

request = SendMessageRequest(
    id=str(uuid4()),
    params=MessageSendParams(
        message={
            "role": "user",
            "parts": [{"kind": "text", "text": "Hello!"}],
            "messageId": uuid4().hex,
        }
    )
)
response = await client.send_message(request)

AI Gateway (Proxy Server)

Step 1. Add your Agent to the AI Gateway

Step 2. Call Agent via A2A SDK

from a2a.client import A2ACardResolver, A2AClient
from a2a.types import MessageSendParams, SendMessageRequest
from uuid import uuid4
import httpx

base_url = "http://localhost:4000/a2a/my-agent"  # LiteLLM proxy + agent name
headers = {"Authorization": "Bearer sk-1234"}    # LiteLLM Virtual Key

async with httpx.AsyncClient(headers=headers) as httpx_client:
    resolver = A2ACardResolver(httpx_client=httpx_client, base_url=base_url)
    agent_card = await resolver.get_agent_card()
    client = A2AClient(httpx_client=httpx_client, agent_card=agent_card)

    request = SendMessageRequest(
        id=str(uuid4()),
        params=MessageSendParams(
            message={
                "role": "user",
                "parts": [{"kind": "text", "text": "Hello!"}],
                "messageId": uuid4().hex,
            }
        )
    )
    response = await client.send_message(request)

Docs: A2A Agent Gateway

MCP Tools - Connect MCP servers to any LLM (Python SDK + AI Gateway)

Python SDK - MCP Bridge

from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client
from litellm import experimental_mcp_client
import litellm

server_params = StdioServerParameters(command="python", args=["mcp_server.py"])

async with stdio_client(server_params) as (read, write):
    async with ClientSession(read, write) as session:
        await session.initialize()

        # Load MCP tools in OpenAI format
        tools = await experimental_mcp_client.load_mcp_tools(session=session, format="openai")

        # Use with any LiteLLM model
        response = await litellm.acompletion(
            model="gpt-4o",
            messages=[{"role": "user", "content": "What's 3 + 5?"}],
            tools=tools
        )

AI Gateway - MCP Gateway

Step 1. Add your MCP Server to the AI Gateway

Step 2. Call MCP tools via /chat/completions

curl -X POST 'http://0.0.0.0:4000/v1/chat/completions' \
  -H 'Authorization: Bearer sk-1234' \
  -H 'Content-Type: application/json' \
  -d '{
    "model": "gpt-4o",
    "messages": [{"role": "user", "content": "Summarize the latest open PR"}],
    "tools": [{
      "type": "mcp",
      "server_url": "litellm_proxy/mcp/github",
      "server_label": "github_mcp",
      "require_approval": "never"
    }]
  }'

Use with Cursor IDE

{
  "mcpServers": {
    "LiteLLM": {
      "url": "http://localhost:4000/mcp/",
      "headers": {
        "x-litellm-api-key": "Bearer sk-1234"
      }
    }
  }
}

Docs: MCP Gateway

Supported Providers (Website Supported Models | Docs)

Provider /chat/completions /messages /responses /embeddings /image/generations /audio/transcriptions /audio/speech /moderations /batches /rerank
Abliteration (abliteration)
AI/ML API (aiml)
AI21 (ai21)
AI21 Chat (ai21_chat)
Aleph Alpha
Amazon Nova
Anthropic (anthropic)
Anthropic Text (anthropic_text)
Anyscale
AssemblyAI (assemblyai)
Auto Router (auto_router)
AWS - Bedrock (bedrock)
AWS - Sagemaker (sagemaker)
Azure (azure)
Azure AI (azure_ai)
Azure Text (azure_text)
Baseten (baseten)
Bytez (bytez)
Cerebras (cerebras)
Clarifai (clarifai)
Cloudflare AI Workers (cloudflare)
Codestral (codestral)
Cohere (cohere)
Cohere Chat (cohere_chat)
CometAPI (cometapi)
CompactifAI (compactifai)
Custom (custom)
Custom OpenAI (custom_openai)
Dashscope (dashscope)
Databricks (databricks)
DataRobot (datarobot)
Deepgram (deepgram)
DeepInfra (deepinfra)
Deepseek (deepseek)
ElevenLabs (elevenlabs)
Empower (empower)
Fal AI (fal_ai)
Featherless AI (featherless_ai)
Fireworks AI (fireworks_ai)
FriendliAI (friendliai)
Galadriel (galadriel)
GitHub Copilot (github_copilot)
GitHub Models (github)
Google - PaLM
Google - Vertex AI (vertex_ai)
Google AI Studio - Gemini (gemini)
GradientAI (gradient_ai)
Groq AI (groq)
Heroku (heroku)
Hosted VLLM (hosted_vllm)
Huggingface (huggingface)
Hyperbolic (hyperbolic)
IBM - Watsonx.ai (watsonx)
Infinity (infinity)
Jina AI (jina_ai)
Lambda AI (lambda_ai)
Lemonade (lemonade)
LiteLLM Proxy (litellm_proxy)
Llamafile (llamafile)
LM Studio (lm_studio)
Maritalk (maritalk)
Meta - Llama API (meta_llama)
Mistral AI API (mistral)
Moonshot (moonshot)
Morph (morph)
Nebius AI Studio (nebius)
NLP Cloud (nlp_cloud)
Novita AI (novita)
Nscale (nscale)
Nvidia NIM (nvidia_nim)
OCI (oci)
Ollama (ollama)
Ollama Chat (ollama_chat)
Oobabooga (oobabooga)
OpenAI (openai)
OpenAI-like (openai_like)
OpenRouter (openrouter)
OVHCloud AI Endpoints (ovhcloud)
Perplexity AI (perplexity)
Petals (petals)
Predibase (predibase)
Recraft (recraft)
Replicate (replicate)
Sagemaker Chat (sagemaker_chat)
Sambanova (sambanova)
Snowflake (snowflake)
Text Completion Codestral (text-completion-codestral)
Text Completion OpenAI (text-completion-openai)
Together AI (together_ai)
Topaz (topaz)
Triton (triton)
V0 (v0)
Vercel AI Gateway (vercel_ai_gateway)
VLLM (vllm)
Volcengine (volcengine)
Voyage AI (voyage)
WandB Inference (wandb)
Watsonx Text (watsonx_text)
xAI (xai)
Xinference (xinference)

Read the Docs


Get Started

You can use LiteLLM through either the Proxy Server or Python SDK. Both give you a unified interface to access multiple LLMs (100+ LLMs). Choose the option that best fits your needs:

LiteLLM AI Gateway LiteLLM Python SDK
Use Case Central service (LLM Gateway) to access multiple LLMs Use LiteLLM directly in your Python code
Who Uses It? Gen AI Enablement / ML Platform Teams Developers building LLM projects
Key Features Centralized API gateway with authentication and authorization, multi-tenant cost tracking and spend management per project/user, per-project customization (logging, guardrails, caching), virtual keys for secure access control, admin dashboard UI for monitoring and management Direct Python library integration in your codebase, Router with retry/fallback logic across multiple deployments (e.g. Azure/OpenAI) - Router, application-level load balancing and cost tracking, exception handling with OpenAI-compatible errors, observability callbacks (Lunary, MLflow, Langfuse, etc.)

Stable Release: Use docker images with the -stable tag. These have undergone 12 hour load tests, before being published. More information about the release cycle here

Support for more providers. Missing a provider or LLM Platform, raise a feature request.

Run in Developer Mode

Services

  1. Setup .env file in root
  2. Run dependant services docker-compose up db prometheus

Backend

  1. (In root) create virtual environment python -m venv .venv
  2. Activate virtual environment source .venv/bin/activate
  3. Install dependencies uv sync --all-extras --group proxy-dev
  4. uv run prisma generate
  5. prisma generate
  6. Start proxy backend python litellm/proxy/proxy_cli.py

Frontend

  1. Navigate to ui/litellm-dashboard
  2. Install dependencies npm install
  3. Run npm run dev to start the dashboard

Verify Docker Image Signatures

All LiteLLM Docker images published to GHCR are signed with cosign. Every release is signed with the same key introduced in commit 0112e53.

Verify using the pinned commit hash (recommended):

A commit hash is cryptographically immutable, so this is the strongest way to ensure you are using the original signing key:

cosign verify \
  --key https://raw.githubusercontent.com/BerriAI/litellm/0112e53046018d726492c814b3644b7d376029d0/cosign.pub \
  ghcr.io/berriai/litellm:<release-tag>

Verify using a release tag (convenience):

Tags are protected in this repository and resolve to the same key. This option is easier to read but relies on tag protection rules:

cosign verify \
  --key https://raw.githubusercontent.com/BerriAI/litellm/<release-tag>/cosign.pub \
  ghcr.io/berriai/litellm:<release-tag>

Replace <release-tag> with the version you are deploying (e.g. v1.83.0-stable).


Enterprise

For companies that need better security, user management and professional support

Get an Enterprise License Talk to founders

This covers:

  • Features under the LiteLLM Commercial License:
  • Feature Prioritization
  • Custom Integrations
  • Professional Support - Dedicated discord + slack
  • Custom SLAs
  • Secure access with Single Sign-On

Contributing

We welcome contributions to LiteLLM! Whether you're fixing bugs, adding features, or improving documentation, we appreciate your help.

Quick Start for Contributors

This requires uv to be installed.

git clone https://github.com/BerriAI/litellm.git
cd litellm
make install-dev    # Install development dependencies
make format         # Format your code
make lint           # Run all linting checks
make test-unit      # Run unit tests
make format-check   # Check formatting only

For detailed contributing guidelines, see CONTRIBUTING.md.

📖 Contributing to documentation? The LiteLLM docs have moved to a separate repository: BerriAI/litellm-docs. Please open doc PRs there. Docs are served at docs.litellm.ai.

Code Quality / Linting

LiteLLM follows the Google Python Style Guide.

Our automated checks include:

  • Black for code formatting
  • Ruff for linting and code quality
  • MyPy for type checking
  • Circular import detection
  • Import safety checks

All these checks must pass before your PR can be merged.

Support / talk with founders

Contributors

S
Description
Python SDK, Proxy Server (AI Gateway) to call 100+ LLM APIs in OpenAI (or native) format, with cost tracking, guardrails, loadbalancing and logging. [Bedrock, Azure, OpenAI, VertexAI, Cohere, Anthropic, Sagemaker, HuggingFace, VLLM, NVIDIA NIM]
Readme MIT
1.1 GiB
Languages
Python 81%
TypeScript 12.2%
JavaScript 5.9%
HTML 0.5%
HCL 0.2%