Understanding the Flux State Machine

Emitted events adhere to the below state machine for managing turns:

Update messages are sent for approximately every 0.25 seconds of transcribed audio, regardless of transcript updates, unless a state change has occurred.
An EagerEndOfTurn message always contains a nonempty transcript.
A TurnResumed message can only follow a preceding EagerEndOfTurn message.
The EndOfTurn transcript will always match the immediately preceding EagerEndOfTurn transcript. If the transcript changes after an EagerEndOfTurn, a TurnResumed event will occur first.
The turn_index increments immediately following an EndOfTurn message.
When using flux-general-multi, all TurnInfo events include languages (detected languages sorted by word count) and languages_hinted (active language hints). See Language Prompting.
Every EndOfTurn event includes a trigger field — model (native detection), manual (ForceEndTurn), or timeout (eot_timeout_ms) — indicating what ended the turn.
You can end the current turn at any time by sending a ForceEndTurn message. Flux emits an EndOfTurn with trigger: "manual" from any in-turn state.

Configuring Event Behavior: The EagerEndOfTurn and TurnResumed events are only triggered when you set the eager_eot_threshold parameter. The EndOfTurn event behavior is controlled by eot_threshold and eot_timeout_ms parameters. See the End-of-Turn Configuration for details on tuning these thresholds for your use case.

Barge-in and audio quality: Flux’s StartOfTurn event is the recommended way to trigger barge-in — it’s more reliable than an external VAD because every StartOfTurn is guaranteed to contain a non-empty transcript. For guidance on echo cancellation, noise suppression, and other audio preprocessing that affects turn detection, see Audio Preprocessing & Barge-In.

Turn Lifecycle Example

Here’s how Flux processes a customer calling support saying “Hi I need to cancel my subscription please.”

Notice how confidence builds up and how the EagerEndOfTurn event fires before the final EndOfTurn. With EagerEndOfTurn, your voice agent can begin preparing a response before the user has fully finished speaking. This allows you to send a synchronous request with early context, creating the effect of a faster, more natural reply.

{
  "event": "Update",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 0.2,
  "transcript": "",
  "words": [],
  "end_of_turn_confidence": 0.1
}
{
  "event": "Update",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 0.5,
  "transcript": "",
  "words": [],
  "end_of_turn_confidence": 0.1
}
{
  "event": "StartOfTurn",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 0.6,
  "transcript": "Hi I",
  "words": [
    {
      "word": "Hi",
      "confidence": 0.95,
      "start": 0.42,
      "end": 0.56
    },
    {
      "word": "I",
      "confidence": 0.92,
      "start": 0.56,
      "end": 0.6
    }
  ],
  "end_of_turn_confidence": 0.1
}
{
  "event": "Update",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 0.8,
  "transcript": "Hi I need to",
  "words": [...],
  "end_of_turn_confidence": 0.1
}
{
  "event": "Update",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 1.0,
  "transcript": "Hi I need to cancel my subscription.",
  "words": [...],
  "end_of_turn_confidence": 0.3
}
{
  "event": "EagerEndOfTurn",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 1.1,
  "transcript": "Hi I need to cancel my subscription.",
  "words": [...],
  "end_of_turn_confidence": 0.3
}
{
  "event": "TurnResumed",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 1.2,
  "transcript": "Hi I need to cancel my subscription please",
  "words": [...],
  "end_of_turn_confidence": 0.1
}
{
  "event": "Update",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 1.4,
  "transcript": "Hi I need to cancel my subscription please.",
  "words": [...],
  "end_of_turn_confidence": 0.3
}
{
  "event": "EagerEndOfTurn",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 1.5,
  "transcript": "Hi I need to cancel my subscription please.",
  "words": [...],
  "end_of_turn_confidence": 0.3
}
{
  "event": "Update",
  "turn_index": 0,
  "audio_window_start": 0.1,
  "audio_window_end": 1.6,
  "transcript": "Hi I need to cancel my subscription please.",
  "words": [...],
  "end_of_turn_confidence": 0.5
}
{
  "event": "EndOfTurn",
  "turn_index": 0,
  "audio_window_start": 0.0,
  "audio_window_end": 1.7,
  "transcript": "Hi I need to cancel my subscription please.",
  "words": [...],
  "end_of_turn_confidence": 0.7,
  "trigger": "model"
}