lm-sys / lm-sys/FastChat

vllm_worker is incompatible with vllm > 0.8.x

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Description

While this works on VLLM 0.7.x, the latest one (0.8.2), which supports mistral-small and gemma, does not seem have the "engine" attribute:

```python
2025-03-24 22:04:27 | ERROR | stderr | Traceback (most recent call last):
2025-03-24 22:04:27 | ERROR | stderr | File "/p/haicluster/llama/FastChat/fastchat/serve/vllm_worker.py", line 291, in
2025-03-24 22:04:27 | ERROR | stderr | worker = VLLMWorker(
2025-03-24 22:04:27 | ERROR | stderr | ^^^^^^^^^^^
2025-03-24 22:04:27 | ERROR | stderr | File "/p/haicluster/llama/FastChat/fastchat/serve/vllm_worker.py", line 57, in __init__
2025-03-24 22:04:27 | ERROR | stderr | self.tokenizer = llm_engine.engine.tokenizer
2025-03-24 22:04:27 | ERROR | stderr | ^^^^^^^^^^^^^^^^^
2025-03-24 22:04:27 | ERROR | stderr | AttributeError: 'AsyncLLM' object has no attribute 'engine'
```

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start in fastchat/serve/vllm_worker.py around line 57, where initialization accesses llm_engine.engine.tokenizer, and compare the VLLM 0.7.x and 0.8.2 behavior described in the traceback. Confirm the worker can initialize with VLLM 0.8.2 without the missing-attribute error while preserving the tokenizer setup.

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Assessment

Tech stack
python
Domain
ai
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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