[Feature]: Support Anthropic API `/v1/messages` endpoint

[mgoin]

🚀 The feature, motivation and pitch

We need to add support for Anthropic API, at least for the /v1/messages endpoint, in order to support applications that depend on it like Claude Code.

There are routers that implement the endpoint by wrapping the OpenAI api server from vLLM, like https://github.com/musistudio/claude-code-router and https://github.com/1rgs/claude-code-proxy

I'm not sure the difficulty, but I think it shouldn't be difficult and hopefully should be able to be added as a new endpoint within vllm serve

Alternatives

No response

Additional context

No response

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[oddgarden6465]

I would love to contribute!

[kyle-compute]

Hey, saw this wasn’t assigned :D

I’ve been using vLLM a bit recently (and this feature would help me out so I'm willing to do it myself)

Planning to implement /v1/messages support for Anthropic-style requests:
-Add route to api_server.py or separate anthropic_router.
-Map Anthropic inputs to ChatCompletionRequest, reuse engine.
-Return responses in Anthropic format (non-stream + SSE for streaming)
-Add unit tests for both modes

Let me know if there’s a preferred spot for the route or anything I should watch for before opening a PR, I read the contributing docs but maybe something wasn't mentioned

I'd appreciate being assigned for visibility

[ziozzang]

+1

wait for using claude code with vllm.

[scwgoire]

Guys, maybe you have already been thinking about this, but why would we want the OpenAI and Anthropic endpoints not to be available in the same vLLM process ? I feel like the model a user would want to serve would likely be the same whether his "clients" use it through an OpenAI or Anthropic API. Thus, it would be legitimate to want a single vLLM serving both APIs because one's "clients" use both openai-compatible tools and anthropic-compatible tools.

My knowledge of the vLLM codebase is very shallow so you may very well say it would be too complex to be worth it.

On the other hand, there is a possibility you started working on this without thinking about this (entrypoints/openai naturally leads to entrypoints/anthropic), so I though you might find the idea interesting 🤷 😄

[mgoin]

Now that #22627 and #27882 have landed, you can run vllm serve to host your own model and get /v1/messages to run with claude code directly! This will be in the next release

vllm serve Qwen/Qwen3-4B-Instruct-2507 --served-model-name my-model --enable-auto-tool-choice --tool-call-parser hermes
ANTHROPIC_API_KEY="dummy" ANTHROPIC_BASE_URL="http://localhost:8000" claude --model my-model

[hellangleZ]

Now that #22627 and #27882 have landed, you can run vllm serve to host your own model and get /v1/messages to run with claude code directly! This will be in the next release

vllm serve Qwen/Qwen3-4B-Instruct-2507 --served-model-name my-model --enable-auto-tool-choice --tool-call-parser hermes
ANTHROPIC_API_KEY="dummy" ANTHROPIC_BASE_URL="http://localhost:8000" claude --model my-model

which version, 0.12.1?