Voice Agent Latency Testing: Where the Clock Starts

Voice agent latency testing should measure the delay a caller experiences from the end of their speech to an audible or complete agent response, with explicitly named start and stop events because different measurement boundaries can produce incomparable results for the same system. Measuring from caller speech end includes endpointing, transport, processing, model, and synthesis delays, whereas later start points such as final transcription or model request exclude parts of the wait experienced by callers. First audible audio and answer completion should be reported separately, since filler phrases can improve perceived responsiveness without reducing time to a useful answer. ITU-T G.114 offers transmission-delay guidance for telephony but does not establish response-time targets for voice agents or agent reasoning, so applying its mouth-to-ear figures to agent turns requires careful scope disclosure. Reports should prioritize distributions, including medians and upper percentiles, over averages; include sample sizes, slow-turn details, call paths, concurrency levels, and versioned metric definitions; and test across increasing concurrent call loads, since tail latency often worsens before averages or error rates reveal a problem.

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