---
id: pr-flash-attention-2544
repo: Dao-AILab/flash-attention
pr: 2544
title: '[CuTe,Bwd] guard softcap for varlen backward'
author: reubenconducts
date: '2026-05-07'
url: https://github.com/Dao-AILab/flash-attention/pull/2544
source_category: upstream-code
architectures:
- sm100
tags:
- cute
techniques: []
hardware_features: []
kernel_types:
- attention
languages:
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: 9192248e4a61b75629258d151ea45ad0e0161ff5
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- flash_attn/cute/interface.py
- tests/cute/test_flash_attn.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2544
head_ref_oid: 3e2ce19c52eeaed38281cd7b9dcd24502612a3b9
---
# [CuTe,Bwd] guard softcap for varlen backward

- Repository: `Dao-AILab/flash-attention`
- PR: [2544](https://github.com/Dao-AILab/flash-attention/pull/2544)
- 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/interface.py`
- `tests/cute/test_flash_attn.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2544`
