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       "start": 0.42,
32       "end": 0.56
33     },
34     {
35       "word": "I",
36       "confidence": 0.92,
37       "start": 0.56,
38       "end": 0.6
39     }
40   ],
41   "end_of_turn_confidence": 0.1
42 }
43 
44 {
45   "event": "Update",
46   "turn_index": 0,
47   "audio_window_start": 0.0,
48   "audio_window_end": 0.8,
49   "transcript": "Hi I need to",
50   "words": [...],
51   "end_of_turn_confidence": 0.1
52 }
53 
54 {
55   "event": "Update",
56   "turn_index": 0,
57   "audio_window_start": 0.0,
58   "audio_window_end": 1.0,
59   "transcript": "Hi I need to cancel my subscription.",
60   "words": [...],
61   "end_of_turn_confidence": 0.3
62 }
63 
64 {
65   "event": "EagerEndOfTurn",
66   "turn_index": 0,
67   "audio_window_start": 0.0,
68   "audio_window_end": 1.1,
69   "transcript": "Hi I need to cancel my subscription.",
70   "words": [...],
71   "end_of_turn_confidence": 0.3
72 }
73 
74 {
75   "event": "TurnResumed",
76   "turn_index": 0,
77   "audio_window_start": 0.0,
78   "audio_window_end": 1.2,
79   "transcript": "Hi I need to cancel my subscription please",
80   "words": [...],
81   "end_of_turn_confidence": 0.1
82 }
83 
84 {
85   "event": "Update",
86   "turn_index": 0,
87   "audio_window_start": 0.0,
88   "audio_window_end": 1.4,
89   "transcript": "Hi I need to cancel my subscription please.",
90   "words": [...],
91   "end_of_turn_confidence": 0.3
92 }
93 
94 {
95   "event": "EagerEndOfTurn",
96   "turn_index": 0,
97   "audio_window_start": 0.0,
98   "audio_window_end": 1.5,
99   "transcript": "Hi I need to cancel my subscription please.",
100   "words": [...],
101   "end_of_turn_confidence": 0.3
102 }
103 
104 {
105   "event": "Update",
106   "turn_index": 0,
107   "audio_window_start": 0.1,
108   "audio_window_end": 1.6,
109   "transcript": "Hi I need to cancel my subscription please.",
110   "words": [...],
111   "end_of_turn_confidence": 0.5
112 }
113 
114 {
115   "event": "EndOfTurn",
116   "turn_index": 0,
117   "audio_window_start": 0.0,
118   "audio_window_end": 1.7,
119   "transcript": "Hi I need to cancel my subscription please.",
120   "words": [...],
121   "end_of_turn_confidence": 0.7
122 }