# B12X Linear Backend

[B12X](https://pypi.org/project/b12x/) provides optional CUDA kernels for
NVIDIA SM120 and SM121 GPUs. Install the dependency with:

```bash
uv pip install "vllm[b12x]"
```

B12X participates in automatic kernel selection after established optimized
backends and before emulation. Select it explicitly with:

```bash
vllm serve <model> --linear-backend b12x
```

## Supported Configurations

| Backend | Supported configurations |
| ------- | ------------------------ |
| Linear | Per-tensor FP8, 128x128 block FP8, MXFP8, NVFP4, and MXFP4 |

Dense W4A16 layers are not handled by B12X and continue to use another
compatible backend such as Marlin.