Check actual latency

You can monitor the latency of individual calls in Call History.

Call history page showing per-call latency metrics — Call History

Understanding latency metrics

End-to-end latency measures the total time from when the user stops speaking until the AI agent begins responding. This includes processing time, network delays, and model inference time.

Key metrics explained

P90 (90th Percentile): 90% of calls have latency below this value.
Median (50th Percentile): Half of the calls have latency less than this value.
Min: The fastest response time achieved in any call.

Retrieve latency via the API

You can also retrieve detailed latency breakdowns programmatically using the Get Call API. After a call ends, the response includes a latency object with per-component metrics.

curl -X GET "https://api.retellai.com/v2/get-call/CALL_ID" \
  -H "Authorization: Bearer YOUR_API_KEY"

from retell import Retell

client = Retell(api_key="YOUR_API_KEY")
call = client.call.retrieve("CALL_ID")
print(call.latency)

import Retell from "retell-ai";

const client = new Retell({ apiKey: "YOUR_API_KEY" });
const call = await client.call.retrieve("CALL_ID");
console.log(call.latency);

Latency breakdown fields

The latency object contains the following components. Not all fields are present on every call — availability depends on the call type and features used.

Field	Description
`e2e`	End-to-end latency from when the user stops talking to when the agent starts talking. Does not account for network trip time from the Retell server to the user’s frontend.
`asr`	Transcription latency — the difference between the duration of audio chunks streamed and the duration of the transcribed portion.
`llm`	LLM latency from the start of the LLM call to the first speakable chunk received. When using a custom LLM, this includes the websocket roundtrip time.
`llm_websocket_network_rtt`	Websocket roundtrip latency between your server and the Retell server. Only populated for calls using a custom LLM.
`tts`	Text-to-speech latency from triggering TTS to the first audio byte received.
`knowledge_base`	Knowledge base retrieval latency from triggering retrieval to receiving all relevant context. Only populated when the agent uses the knowledge base feature.
`s2s`	Speech-to-speech latency from requesting a response to the first byte received. Only populated for calls using a speech-to-speech model (e.g., Realtime API).

Each component is an object with these statistical fields:

Field	Type	Description
`p50`	number	50th percentile (median) latency in milliseconds
`p90`	number	90th percentile latency in milliseconds
`p95`	number	95th percentile latency in milliseconds
`p99`	number	99th percentile latency in milliseconds
`min`	number	Minimum latency in milliseconds
`max`	number	Maximum latency in milliseconds
`num`	number	Number of data points tracked
`values`	number[]	All individual latency data points in milliseconds

Example response

Here is an example of the latency portion of a Get Call response:

{
  "latency": {
    "e2e": {
      "p50": 800,
      "p90": 1200,
      "p95": 1500,
      "p99": 2500,
      "min": 500,
      "max": 2700,
      "num": 10,
      "values": [500, 620, 780, 800, 850, 900, 1100, 1200, 1500, 2700]
    },
    "llm": {
      "p50": 400,
      "p90": 650,
      "p95": 800,
      "p99": 1200,
      "min": 250,
      "max": 1300,
      "num": 10,
      "values": [250, 310, 380, 400, 420, 500, 600, 650, 800, 1300]
    },
    "tts": {
      "p50": 150,
      "p90": 250,
      "p95": 300,
      "p99": 400,
      "min": 80,
      "max": 420,
      "num": 10,
      "values": [80, 100, 130, 150, 160, 200, 230, 250, 300, 420]
    }
  }
}

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Check actual latency

Understanding latency metrics

Key metrics explained

Retrieve latency via the API

Latency breakdown fields

Example response

​Understanding latency metrics

​Key metrics explained

​Retrieve latency via the API

​Latency breakdown fields

​Example response

Understanding latency metrics

Key metrics explained

Retrieve latency via the API

Latency breakdown fields

Example response