Quick interview answer
Decompose request paths by stage, task slice, retries, and token usage; do not infer tail behavior from averages.
Detailed explanation
Inspect queue time, retrieval fan-out, context length, tool loops, retry amplification, and provider throttling. Separate time to first token from total completion time. Cost per successful task includes failed attempts and retries, so determine whether declining success is inflating the denominator-adjusted metric. Use traces and controlled load tests to identify saturation and enforce bounded work.
Real-world example
A small group of long-document requests triggers repeated tool calls, increasing both tail latency and total spend while typical requests remain unchanged.
Interview tip
Do not add stage p99 values and call the result end-to-end p99; use correlated traces.
