How a session works

A live session is one stream of audio and everything transcribed from it.

Lifecycle

1. Create the session: POST /v2/live with its options. It answers the session id and a WebSocket url, valid 60 seconds.
2. Connect to the url. With messages_config.receive_lifecycle_events, a start_recording message says the session is ready.
3. Stream the audio, as binary frames or audio_chunk messages. Transcripts arrive as the audio is processed.
4. Stop with {"type": "stop_recording"}. The server transcribes what is left, sends end_recording, the post-processing results (post_transcript, post_final_transcript), end_session, then closes the connection with code 1000.

A session also stops after 60 seconds without audio, and when it reaches its maximum duration (Limits).

Utterances

The audio is cut into utterances at pauses (Endpointing). Each utterance has an id, <channel>_<index> (00_00000003), stable for the whole session. While it is spoken you receive partial transcripts (is_final: false, with receive_partial_transcripts), each replacing the previous one; when it ends, one final transcript (is_final: true).

{
  "type": "transcript",
  "session_id": "0199d7a2-5c3e-7b41-9f0a-3c2d1e4f5a6b",
  "created_at": "2026-10-12T09:04:19.000Z",
  "data": {
    "id": "00_00000003",
    "is_final": true,
    "utterance": {
      "text": "I'd like to change my delivery address.",
      "start": 12.48,
      "end": 14.9,
      "language": "en",
      "confidence": 0.94,
      "channel": 0,
      "words": [{ "word": "I'd", "start": 12.48, "end": 12.62, "confidence": 0.97 }]
    }
  }
}

The features you turn on add their own messages right after each final (translation, entities, redacted data, sentiment), named by the same utterance id.

Choosing your messages

messages_config in the init body selects what comes on the WebSocket:

option	messages	default
receive_partial_transcripts	transcript with is_final: false	false
receive_final_transcripts	transcript with is_final: true	true
receive_speech_events	speech_start, speech_end	true
receive_realtime_processing_events	translation, named_entity_recognition, sentiment_analysis	true
receive_post_processing_events	post_transcript, post_final_transcript	true
receive_acknowledgments	audio_chunk, stop_recording acknowledgments	true
receive_lifecycle_events	start_recording, end_recording, end_session	false
receive_errors	error	true

pii and end_of_turn messages come whenever their feature is on. Every message type is described in the API reference. The same messages can also go to your server (Callbacks).

After the session

GET /v2/live/{id} returns the session’s options and, once it is done, its result: every final utterance, the full transcript and the translations. Sessions stay in your history for your account’s retention (Data retention).