Cursor Open-Sources Mixture-of-Kittens MoE Training Kernel

Cursor open-sourced Mixture-of-Kittens on August 4. The kernel trains Cursor's Composer model across tens of thousands of GPUs on Nvidia's NVL72 racks, per Cursor's blog post.

The kernel fuses every MoE communication and computation step into one deterministic pass, so identical training runs produce identical results. That determinism turns a stalled or diverging run into something bisectable, like a code regression, instead of a mystery.

The code is Apache-2.0 licensed and built from scratch for NVL72 hardware. The GitHub repo went public July 29 and sat at 326 stars by August 5.

The blog post doesn't say how the kernel performs on anything other than NVL72, only that it's written to be modified for other hardware.

That framing is a bet: coding agents, not human engineers, will be the ones who actually port the kernel to other hardware. Watch for who submits the first non-Nvidia fork, and whether it's a person or a bot doing the work.