---
id: pr-flash-attention-2275
repo: Dao-AILab/flash-attention
pr: 2275
title: '[CuteDSL][SM90] varlen bwd works'
author: KareemMusleh
date: '2026-03-10'
url: https://github.com/Dao-AILab/flash-attention/pull/2275
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: e3dd324e6dae3e412c4349cf85dd35fe72568a7a
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- flash_attn/cute/flash_bwd_sm90.py
- flash_attn/cute/interface.py
- tests/cute/test_flash_attn_varlen.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2275
head_ref_oid: 73b9fc659c3c43daa32b2e97c18fe24815614587
---
# [CuteDSL][SM90] varlen bwd works

- Repository: `Dao-AILab/flash-attention`
- PR: [2275](https://github.com/Dao-AILab/flash-attention/pull/2275)
- 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`
- `flash_attn/cute/interface.py`
- `tests/cute/test_flash_attn_varlen.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2275`
