With 98% Cache Hits in Coding, 400-600 t/s Prefill Already Hits Diminishing Returns

nomorebuttsplz · reddit · 2026-09-03

A Reddit user analyzes which workloads are actually prefill-bound: in opencode coding sessions, cache hit rates are 98%, so 400-600 t/s prefill is sufficient—decode takes 75-90% of the time, and even instant prefill would boost throughput by at most 25%. He also notes low cache hit rate doesn't imply prefill bottleneck: a research agent run on GLM 5.3 with only 150 t/s prefill and single-digit cache hits still spends 90%+ of time decoding at just 15 t/s in max mode. He's asking what real workloads remain prefill-bound.

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