300M triangles and 10k skinned characters in the browser via WebGPU

I just stumbled across this on X and was pretty blown away. I didn't think WebGPU was at the stage where it could handle 300M triangles and 10k skinned instances in a single tab without the browser just giving up.

It looks like it's a custom engine using a full meshlet pipeline.

Does anyone know if there's a technical deep-dive on how they're handling the cluster culling or if they're using a visibility buffer?