---
id: pr-vllm-20699
repo: vllm-project/vllm
pr: 20699
title: '[Misc] Log the reason for falling back to FlexAttention'
author: DarkLight1337
date: '2025-07-14'
url: https://github.com/vllm-project/vllm/pull/20699
source_category: upstream-code
architectures:
- sm100
tags: []
techniques: []
hardware_features: []
kernel_types: []
languages: []
captured_at: '2026-05-16'
status: merged
merge_sha: e8cc53af5e17205470c04f442e67f276e08623a1
inclusion_reason: defer
changed_paths:
- vllm/attention/selector.py
- vllm/platforms/cuda.py
- vllm/reasoning/hunyuan_a13b_reasoning_parser.py
- vllm/v1/attention/backends/cpu_attn.py
- vllm/v1/attention/backends/flash_attn.py
- vllm/v1/attention/backends/flashinfer.py
- vllm/v1/attention/backends/flex_attention.py
- vllm/v1/attention/backends/mla/common.py
- vllm/v1/attention/backends/rocm_aiter_fa.py
- vllm/v1/attention/backends/triton_attn.py
artifact_dir: evidence/pull-bundles/vllm/gh-20699
head_ref_oid: 14c86029f8524206406bef02763b707d676a2ed1
---
# [Misc] Log the reason for falling back to FlexAttention

- Repository: `vllm-project/vllm`
- PR: [20699](https://github.com/vllm-project/vllm/pull/20699)
- Decision: `defer`
- Reason: defer

## Changed Paths

- `vllm/attention/selector.py`
- `vllm/platforms/cuda.py`
- `vllm/reasoning/hunyuan_a13b_reasoning_parser.py`
- `vllm/v1/attention/backends/cpu_attn.py`
- `vllm/v1/attention/backends/flash_attn.py`
- `vllm/v1/attention/backends/flashinfer.py`
- `vllm/v1/attention/backends/flex_attention.py`
- `vllm/v1/attention/backends/mla/common.py`
- `vllm/v1/attention/backends/rocm_aiter_fa.py`
- `vllm/v1/attention/backends/triton_attn.py`

## Evidence Bundle

`evidence/pull-bundles/vllm/gh-20699`
