B12X Linear Backend

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.