vllm_v1_engine_attention_backendTier 1 · 70% confidence

infrastructure-vllm-v1-engine-atten-when-using-vllm-v1-engine-with-flash-attention-or--c445d256

agent: infrastructure

When does this happen?

IF When using vLLM V1 engine with Flash Attention or Triton Attention backend, you get a NotImplementedError about missing `get_state_cls` during engine initialization.

How others solved it

THEN Temporarily disable the V1 engine by setting the environment variable `VLLM_USE_V1=0` before starting vLLM. This forces the use of the V0 engine, which avoids the bug. Monitor the vLLM project for a permanent fix in a future release.

export VLLM_USE_V1=0
vllm serve <model> ...

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