Kernel fusion lifts GLM 5.3 Flash to 40 tok/s

GLM 5.3 Flash was decoding at just 59% of an M3 Ultra's memory bandwidth, according to the maintainer's GLM 5.3 Flash benchmark post.

Idle bandwidth on hardware that's already paid for. The fix took decode speed from 29 to 40 tokens per second.

The big weight-streaming kernels weren't the issue. Dozens of smaller kernels ran between them, and each one paid its own dispatch latency.

Fusing that in-between work into larger dispatches raised decode speed at every context length tested. At 62k context, speed measured 24 to 38 tokens per second. A Claude Code harness run at 200k depth averaged over 38 t/s under the same fix.

That's 81% of the chip's bandwidth ceiling, up from 59%. On Apple Silicon, once weights stream fast enough, dispatch count becomes the limit.

The maintainer's post doesn't say whether the fusion technique generalizes to other models or depends on the q4 quantization path used here.