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Same KV pool: vLLM wins TTFT, SGLang never freezes a stream, and P99 ITL barely differs. Explain it and fix both.

A head-to-head benchmark at the same pool size says vLLM starts answers faster and the two engines tie on P99 inter-token latency, yet users report frozen streams on one of them. The answer traces both tails to admission and preemption, shows why P99 ITL cannot see a freeze, and fixes each engine with one setting.

Updated Nov 2026 · Worked answers on inference mechanisms, with calculations, implementation details, and follow-up questions.

A head-to-head benchmark at the same pool size says vLLM starts answers faster and the two engines tie on P99 inter-token latency, yet users report frozen streams on one of them. The answer traces both tails to admission and preemption, shows why P99 ITL cannot see a freeze, and fixes each engine with one setting.

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