Lanson Flow (dev)

Configure session parameters via session.update messages.

When to configure

After connect: send session.update right after receiving session.created

During session: update parameters at any time

Confirmation: server returns session.updated to confirm

All options

Language and context

| Field | Type | Description | |---|---|---| | language | string | Audio source language (e.g. zh, en, auto) | | prompt | string | Context hint, max 2000 characters |

Model selection

| Field | Snake-case alias | Description | |---|---|---| | backend | — | Upstream backend selection | | sttModel | stt_model | STT model | | normalizerModel | normalizer_model | Text normalizer model |

VAD configuration

| Field | Snake-case alias | Type | Description | |---|---|---|---| | vad | — | boolean | Enable VAD | | vadThreshold | vad_threshold | number | Sensitivity threshold | | vadSilenceMs | vad_silence_ms | number | Silence duration to trigger end-of-speech | | vadPrefixMs | vad_prefix_ms | number | Prefix padding | | vadMinSpeechMs | vad_min_speech_ms | number | Minimum speech segment | | vadTargetSpeechMs | vad_target_speech_ms | number | Target speech segment | | vadMaxSpeechMs | vad_max_speech_ms | number | Maximum speech segment | | vadSmartSplitWindowMs | vad_smart_split_window_ms | number | Smart split window |

Audio configuration

Fixed by the gateway, client cannot change:

{ "format": "pcm_s16le", "sample_rate": 16000, "channels": 1 }

Examples

Set language

{ "type": "session.update", "language": "zh" }

Set context hint

{ "type": "session.update", "prompt": "Cardiology conference, terms: atrial fibrillation, anticoagulation, warfarin" }

Adjust VAD

{
  "type": "session.update",
  "vad": true,
  "vadThreshold": 0.5,
  "vadSilenceMs": 800
}

Switch language at runtime

{ "type": "session.update", "language": "en" }

Tenant isolation

All non-whitelisted fields are stripped before forwarding upstream. These fields are injected by the gateway and cannot be overridden:

request_id

session_id

user_id

[Client Messages](/docs/api-reference/client-messages) — message format

[Server Events](/docs/api-reference/server-events) — session.updated event

[Live Translation](/docs/concepts/live-translation) — translation concepts