Disable FlashInfer sampler by default #26859
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Signed-off-by: mgoin <mgoin64@gmail.com>
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This pull request correctly disables the FlashInfer sampler by default, requiring users to opt-in by setting VLLM_USE_FLASHINFER_SAMPLER=1. The change from envs.VLLM_USE_FLASHINFER_SAMPLER is not False to a direct boolean check simplifies the logic and makes the default behavior consistent. The corresponding log message is also appropriately changed from a warning to a debug message. The implementation is sound and improves code clarity.
tlrmchlsmth
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Oct 15, 2025
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Signed-off-by: mgoin <mgoin64@gmail.com> Signed-off-by: bbartels <benjamin@bartels.dev>
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…#26859) (#295) vllm-project/vllm#26859 Signed-off-by: mgoin <mgoin64@gmail.com>
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Purpose
There have been increasing reports of correctness issues or IMA with FlashInfer's top-p & top-k sampling kernel (see #26480 (comment)). For instance, it seems it can generates the same output even when the temperature is quite high (even though the seed is not set). vLLM generates different results (expectedly) once the kernel is disabled.
Since flashinfer-python is a default dep of vLLM CUDA now, many more users would be using this kernel by default. Let us disable it by default for now so users can opt-in
Test Plan
Test Result
Essential Elements of an Effective PR Description Checklist
supported_models.mdandexamplesfor a new model.