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.

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.

1 {
2   "event": "Update",
3   "turn_index": 0,
4   "audio_window_start": 0.0,
5   "audio_window_end": 0.2,
6   "transcript": "",
7   "words": [],
8   "end_of_turn_confidence": 0.1
9 }
10 
11 {
12   "event": "Update",
13   "turn_index": 0,
14   "audio_window_start": 0.0,
15   "audio_window_end": 0.5,
16   "transcript": "",
17   "words": [],
18   "end_of_turn_confidence": 0.1
19 }
20 
21 {
22   "event": "StartOfTurn",
23   "turn_index": 0,
24   "audio_window_start": 0.0,
25   "audio_window_end": 0.6,
26   "transcript": "Hi I",
27   "words": [
28     {
29       "word": "Hi",
30       "confidence": 0.95
31     },
32     {
33       "word": "I",
34       "confidence": 0.92
35     }
36   ],
37   "end_of_turn_confidence": 0.1
38 }
39 
40 {
41   "event": "Update",
42   "turn_index": 0,
43   "audio_window_start": 0.0,
44   "audio_window_end": 0.8,
45   "transcript": "Hi I need to",
46   "words": [...],
47   "end_of_turn_confidence": 0.1
48 }
49 
50 {
51   "event": "Update",
52   "turn_index": 0,
53   "audio_window_start": 0.0,
54   "audio_window_end": 1.0,
55   "transcript": "Hi I need to cancel my subscription.",
56   "words": [...],
57   "end_of_turn_confidence": 0.3
58 }
59 
60 {
61   "event": "EagerEndOfTurn",
62   "turn_index": 0,
63   "audio_window_start": 0.0,
64   "audio_window_end": 1.1,
65   "transcript": "Hi I need to cancel my subscription.",
66   "words": [...],
67   "end_of_turn_confidence": 0.3
68 }
69 
70 {
71   "event": "TurnResumed",
72   "turn_index": 0,
73   "audio_window_start": 0.0,
74   "audio_window_end": 1.2,
75   "transcript": "Hi I need to cancel my subscription please",
76   "words": [...],
77   "end_of_turn_confidence": 0.1
78 }
79 
80 {
81   "event": "Update",
82   "turn_index": 0,
83   "audio_window_start": 0.0,
84   "audio_window_end": 1.4,
85   "transcript": "Hi I need to cancel my subscription please.",
86   "words": [...],
87   "end_of_turn_confidence": 0.3
88 }
89 
90 {
91   "event": "EagerEndOfTurn",
92   "turn_index": 0,
93   "audio_window_start": 0.0,
94   "audio_window_end": 1.5,
95   "transcript": "Hi I need to cancel my subscription please.",
96   "words": [...],
97   "end_of_turn_confidence": 0.3
98 }
99 
100 {
101   "event": "Update",
102   "turn_index": 0,
103   "audio_window_start": 0.1,
104   "audio_window_end": 1.6,
105   "transcript": "Hi I need to cancel my subscription please.",
106   "words": [...],
107   "end_of_turn_confidence": 0.5
108 }
109 
110 {
111   "event": "EndOfTurn",
112   "turn_index": 0,
113   "audio_window_start": 0.0,
114   "audio_window_end": 1.7,
115   "transcript": "Hi I need to cancel my subscription please.",
116   "words": [...],
117   "end_of_turn_confidence": 0.7
118 }