University of Michigan - Ann Arbor

In agentic LLM serving, tail Time to First Token (TTFT) acts as an operational availability boundary rather than a simple latency metric. Although average TTFT may seem manageable across short prompts, worst-case prefill pauses in unoptimized hybrid serving systems often exceed 150 seconds (and can reach hundreds of seconds) during extended multi-turn interactions with tool execution and context modification. These extreme stalls cross client-side timeout thresholds—such as an automated 120-second watchdog in agent platforms or a ten-minute client request timeout—causing client applications to abort and abandon requests. Enforcing an upper bound on tail TTFT (for instance, keeping worst-case turns under 44 seconds) is therefore critical to maintaining service availability in autonomous agent workflows.

Tail Time-to-First-Token as an Agentic Availability Boundary

What target metric upper bound is cited as an example of keeping worst-case turns bounded to maintain service availability in autonomous agent workflows?

Explain why tail Time to First Token (TTFT) functions as an operational availability boundary rather than merely a latency metric in agentic serving workloads.

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