---
id: pr-flash-attention-2433
repo: Dao-AILab/flash-attention
pr: 2433
title: 'Fix: disable 2-CTA backward mode when block_sparse_tensors is used'
author: jduprat
date: '2026-04-03'
url: https://github.com/Dao-AILab/flash-attention/pull/2433
source_category: upstream-code
architectures:
- sm100
tags:
- sm100
techniques: []
hardware_features:
- blackwell
kernel_types:
- attention
languages: []
captured_at: '2026-05-16'
status: merged
merge_sha: 65bfd9a6f27803636e86d75b048da2c13a06c096
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- flash_attn/cute/interface.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2433
head_ref_oid: e35dc56af6b5ae95347b17d2a5b2c674eb4d8ec8
---
# Fix: disable 2-CTA backward mode when block_sparse_tensors is used

- Repository: `Dao-AILab/flash-attention`
- PR: [2433](https://github.com/Dao-AILab/flash-attention/pull/2433)
- 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`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2433`
