Voice Settings

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Three concepts, kept distinct

• Greeting text — inbound_greeting / outbound_greeting. Context text that feeds the {{greeting}} template variable your prompt can reference. It is not spoken automatically. These remain writable via the top-level body fields; inside voice_settings they appear read-only for convenience.
• Opening message — what the assistant literally says first on a call, per direction (inbound_opening_message / outbound_opening_message). Only used in fixed greeting mode.
• Voicemail behavior — voicemail_message. When voicemail is detected: an empty or null value means the assistant hangs up; a non-empty value is spoken to the voicemail, after which the assistant stops.

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Greeting modes

1. fixed mode requires at least one opening message. Switching an existing assistant to fixed keeps its stored messages, so a mode-only update is valid when messages already exist.
2. Opening messages are only accepted while the effective mode is fixed — set greeting_mode: "fixed" in the same request if needed.
3. In fixed mode, sending null for one direction clears it, as long as at least one opening message remains.

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Example

PATCH /v3/assistants/{id}
{
  "voice_settings": {
    "greeting_mode": "fixed",
    "inbound_opening_message": "Thanks for calling Acme — this is Ava. How can I help?",
    "outbound_opening_message": "Hi {{contact.first_name}}, this is Ava from Acme!",
    "voicemail_message": "Sorry we missed you — we'll try again soon."
  }
}

{
  "voice_settings": {
    "greeting_mode": "fixed",
    "inbound_opening_message": "Thanks for calling Acme — this is Ava. How can I help?",
    "outbound_opening_message": "Hi {{contact.first_name}}, this is Ava from Acme!",
    "inbound_greeting": null,
    "outbound_greeting": null,
    "voicemail_message": "Sorry we missed you — we'll try again soon.",
    "enable_voicemail_detection": false
  }
}

​

Notes

• enable_voicemail_detection records intent and is returned on read, but voicemail detection is currently platform-managed — the flag does not yet change runtime behavior.
• Reverting an assistant to a previous version does not restore voice_settings; greeting mode, opening messages, and voicemail behavior keep their current values.