Time to First Token
also: TTFT
How long until the first token of the reply appears — the latency number chat users actually feel.
TTFT spans queueing plus prefill (processing the prompt) — everything before streaming starts. Once tokens flow, users read along happily; before that, they stare at a blank box. Prompt/prefix caching, admission control and shorter contexts buy TTFT; batching efficiency buys tokens/sec. Report both, optimize TTFT first.