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This page walks through the WebSocket message sequence of a streaming session — what the client sends and what the server emits, from session start to termination. For this example, we walk through a user saying: My name is Sonny.

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Session initialization

When the session begins, you receive a Begin message with the session ID and expiration time. 
{
  "type": "Begin",
  "id": "3207b601-2054-48df-ba77-8784dfcf9fb8",
  "expires_at": 1772570132
}

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Speech started

SpeechStarted is emitted only on Universal-3 Pro Streaming. Universal Streaming skips this message and goes straight to the first Turn.
Before any Turn messages are sent, the server sends a SpeechStarted message indicating that speech has been detected. The timestamp field indicates when the speech was detected, in milliseconds relative to the beginning of the audio stream. The confidence field is the confidence score that speech has started. 
{
  "type": "SpeechStarted",
  "timestamp": 1216,
  "confidence": 0.987654
}

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Partial transcript

As the speaker is talking, the server emits one or more Turn messages with end_of_turn: false. These are partial transcripts. 
{
  "turn_order": 0,
  "turn_is_formatted": false,
  "end_of_turn": false,
  "transcript": "My name is—",
  "end_of_turn_confidence": 0,
  "words": [
    {
      "start": 1216,
      "end": 1627,
      "text": "My",
      "confidence": 0.956314,
      "word_is_final": false
    },
    {
      "start": 1668,
      "end": 2490,
      "text": "name",
      "confidence": 0.999393,
      "word_is_final": false
    },
    {
      "start": 2531,
      "end": 3067,
      "text": "is—",
      "confidence": 0.753325,
      "word_is_final": false
    }
  ],
  "utterance": "",
  "type": "Turn"
}
The cadence and shape of partials depends on the model. See Universal-3 Pro Streaming and Universal Streaming for the details of how each model produces partials.

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End of turn

When the turn ends, the server emits a Turn message with end_of_turn: true and the final transcript. 
{
  "turn_order": 0,
  "turn_is_formatted": true,
  "end_of_turn": true,
  "transcript": "My name is Sonny.",
  "end_of_turn_confidence": 1,
  "words": [
    {
      "start": 1216,
      "end": 1635,
      "text": "My",
      "confidence": 0.956583,
      "word_is_final": true
    },
    {
      "start": 1676,
      "end": 2515,
      "text": "name",
      "confidence": 0.999199,
      "word_is_final": true
    },
    {
      "start": 2556,
      "end": 2975,
      "text": "is",
      "confidence": 0.999535,
      "word_is_final": true
    },
    {
      "start": 3016,
      "end": 4155,
      "text": "Sonny.",
      "confidence": 0.316031,
      "word_is_final": true
    }
  ],
  "utterance": "My name is Sonny.",
  "type": "Turn"
}

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Keep alive

KeepAlive messages are not required. By default, sessions remain open until explicitly terminated or until the 3-hour maximum session duration is reached. KeepAlive is only relevant if you have configured the inactivity_timeout connection parameter, which closes the session after a period of no audio or messages being sent. If you are using inactivity_timeout and want to keep the session open during periods where no audio is being sent, send a KeepAlive message to reset the inactivity timer: 
{ "type": "KeepAlive" }

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Session termination

To end a session, the client must send a Terminate message. The server then responds with a Termination message containing the total audio and session durations, and closes the connection. Client sends: 
{ "type": "Terminate" }
Server responds: 
{
  "type": "Termination",
  "audio_duration_seconds": 13,
  "session_duration_seconds": 13
}
After receiving the Termination message, no further messages will be sent and the WebSocket connection will be closed.
If Streaming Diarization is enabled (speaker_labels: true), the server may emit a SpeakerRevision message immediately before Termination. The end-of-session refinement adds approximately 400ms of latency at session close. See Revised speaker labels for the message schema and consumption guidance.
Always terminate sessions explicitly. Streaming is billed per session — sessions that are not terminated remain open and continue to accrue charges until the server auto-closes them after 3 hours (error code 3008). See Common errors for more details.