---
id: pr-flash-attention-2158
repo: Dao-AILab/flash-attention
pr: 2158
title: '[CUTE][SM90] GQA backward non deterministic'
author: drisspg
date: '2026-01-10'
url: https://github.com/Dao-AILab/flash-attention/pull/2158
source_category: upstream-code
architectures:
- sm90
tags:
- sm90
techniques: []
hardware_features:
- hopper
kernel_types:
- attention
languages:
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: 5d4c9537a1e0f1adcc3e4c3e11ae46fe94a18b11
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- flash_attn/cute/flash_bwd_sm90.py
- tests/cute/test_flash_attn.py
- tests/cute/test_mask_mod.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2158
head_ref_oid: aec756613a02782f44c4801522b6f2cc041a663f
---
# [CUTE][SM90] GQA backward non deterministic

- Repository: `Dao-AILab/flash-attention`
- PR: [2158](https://github.com/Dao-AILab/flash-attention/pull/2158)
- Decision: `Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.`
- Reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.

## Changed Paths

- `flash_attn/cute/flash_bwd_sm90.py`
- `tests/cute/test_flash_attn.py`
- `tests/cute/test_mask_mod.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2158`
