DeepSeek V4.1 Flash Q4 hits 40 t/s on M3 Ultra with native DSpark multi-token prediction

DeepSeek V4.1F Q4 on M3 Ultra with native DSpark MTP (40tps / 800tps)

A developer forked ds4 and tuned it for DeepSeek V4.1 Flash Q4 on a 512 GB M3 Ultra, lifting decode from 16.6 t/s to 31.3 t/s, and to 40.5 t/s with DSpark speculative decoding. The ~300 GB Q4 weights fit only the 512 GB M3 Ultra. The speedup comes from cutting Metal dispatch overhead: the 384-expert router went from 9 dispatches to 1, the shared expert gate+up+SwiGLU became a single kernel, and BF16 rounding moved inside producer kernels, removing ~770 re-round dispatches. At 300k context, compressed attention selection was the bottleneck; the fix scores only admitted blocks and uses a bounded radix select, keeping decode at 90% of the 8k rate. DSpark verifies 6 tokens per step with shared weight streams and overlapped Engram fetches, dropping verify latency from 177 ms to 112 ms. Output is byte-identical to upstream under greedy decode, with SHA-256 manifests provided. The branch is M3 Ultra only because the optimizations rely on measured behavior of this specific chip's dual-die memory, 80-core GPU scheduling, and Metal dispatch characteristics.

Why it matters: A solid local-inference optimization post: DeepSeek V4.1 Flash Q4 on M3 Ultra goes from 16tps to 40tps via Metal command-buffer merging and native DSpark speculative decoding. Concrete technical detail, directly useful for the local-LLM crowd. Score stays at 72 because the aud...