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A load test says TTFT got faster when we doubled concurrency. What is wrong with the benchmark?

Two runs of one benchmark, the second at twice the concurrency, and the second reaches the first token sooner. The server did not improve. The answer finds the state the first run left behind, shows why it vanishes in a larger run, and lists the client defaults that change the workload.

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

Two runs of one benchmark, the second at twice the concurrency, and the second reaches the first token sooner. The server did not improve. The answer finds the state the first run left behind, shows why it vanishes in a larger run, and lists the client defaults that change the workload.

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