---
id: pr-vllm-38504
repo: vllm-project/vllm
pr: 38504
title: '[Kernels][MoE] Fix legacy_routing to use bitmatrix-based routing path'
author: AndreasKaratzas
date: '2026-04-07'
url: https://github.com/vllm-project/vllm/pull/38504
source_category: upstream-code
architectures:
- sm100
- sm90
tags:
- gemm_quant
- hopper
- moe_routing
- mxfp4
- topk
techniques:
- async-copy
- fine-grained-quantization
- kernel-fusion
hardware_features:
- fp4
- fp8
- hopper
- mxfp4
- tma
kernel_types:
- gemm
- moe
languages:
- cuda-cpp
- triton
captured_at: '2026-05-16'
status: merged
merge_sha: 2df2c85be494d1b98f8a66d0acb7c65f0b119a37
inclusion_reason: Inspect scale layout, accumulator type, tile/schedule choice, epilogue fusion, and partial-tile guards before deriving a candidate.
changed_paths:
- tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-baseline.yaml
- tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-bf16-aiter.yaml
- tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-bf16-triton.yaml
- tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-fp8-triton.yaml
- tests/kernels/moe/test_gpt_oss_triton_kernels.py
- tests/kernels/quantization/test_mxfp4_triton_ep.py
- vllm/model_executor/layers/fused_moe/gpt_oss_triton_kernels_moe.py
artifact_dir: evidence/pull-bundles/vllm/gh-38504
head_ref_oid: 1618fb6fe852f92b578f30310c1beea58c1497bb
---
# [Kernels][MoE] Fix legacy_routing to use bitmatrix-based routing path

- Repository: `vllm-project/vllm`
- PR: [38504](https://github.com/vllm-project/vllm/pull/38504)
- Decision: `Inspect scale layout, accumulator type, tile/schedule choice, epilogue fusion, and partial-tile guards before deriving a candidate.`
- Reason: Inspect scale layout, accumulator type, tile/schedule choice, epilogue fusion, and partial-tile guards before deriving a candidate.

## Changed Paths

- `tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-baseline.yaml`
- `tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-bf16-aiter.yaml`
- `tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-bf16-triton.yaml`
- `tests/evals/gpt_oss/configs/gpt-oss-20b-rocm-quark-mxfp4-fp8-triton.yaml`
- `tests/kernels/moe/test_gpt_oss_triton_kernels.py`
- `tests/kernels/quantization/test_mxfp4_triton_ep.py`
- `vllm/model_executor/layers/fused_moe/gpt_oss_triton_kernels_moe.py`

## Evidence Bundle

`evidence/pull-bundles/vllm/gh-38504`
