Conversation engines

A hosted OpenPhonex AI agent answers the phone with one conversation engine. The default is Standard: speech-to-text, a model, then text-to-speech. You can instead choose GPT-Live 1, which listens and speaks at the same time.

Telephony still uses OpenPhonex numbers and LiveKit. GPT-Live 1 does not send the call to OpenAI SIP.

Choose the engine

In the workspace, open the AI agent and look at Voice. The first control is Conversation engine. The same choice is the first control on the create wizard's voice step.

• Standard keeps separate transcriber, model, and voice rows. Interruptions, acknowledgements, and tool-wait speech stay under your control.
• GPT-Live 1 replaces those three rows with a GPT-Live voice and a backend model for tools. The live model owns barge-in, backchannels, and waiting speech, so acknowledgements and turn-taking stay off for that engine.

GET /v1/agent-catalog lists both engines under conversation_engines. Standard remains the default when you omit the field.

Browser testing

Browser tests involving GPT-Live use the Published snapshot. Publish engine, voice or backend changes before testing them. The test dock names the saved stack that will run, including while you have unsaved engine changes.

API and MCP

The discriminator is voice_frontend: cascade or gpt_live. Omit it and the agent stays Standard.

{
  "voice_frontend": "gpt_live",
  "voice": {
    "provider": "openai",
    "model": "gpt-live-1",
    "voice_id": "marin"
  },
  "model": {
    "provider": "openai",
    "model": "gpt-5.6-luna"
  }
}

POST /v1/agents and PATCH /v1/agents/{agent_id}/voice-stack accept the field. So do MCP create_agent and set_agent_voice_stack.

GET /v1/agents/{agent_id}/voice-stack always returns transcriber, model, and voice. For GPT-Live 1 those are an OpenAI compatibility projection: native captions as the transcriber, the Responses backend as the model, and gpt-live-1 with the selected voice id.

Patching a Standard transcriber onto a GPT-Live agent without switching the engine is refused. Switching back requires voice_frontend: "cascade" and a full Standard stack.

Voices, language, and opening

GPT-Live voices are independent of spoken language. Do not filter them through Standard text-to-speech tables. Language is prompt guidance: the agent follows the caller by default. Opening language is configurable and does not lock the rest of the call.

The opening message is intent, not a script. GPT-Live paraphrases it.

Phone and browser Talk workflow runs cannot use GPT-Live. OpenPhonex rejects that combination before reserving call funds or dispatching media. Ordinary GPT-Live calls and text workflow simulations remain available.

Call evidence

GPT-Live saves native captions and full-call recordings when recording is enabled. Captions can be imperfect, especially across languages. Per-turn audio clips and some timing evidence can be incomplete even when the full recording is available. Check the call's evidence status before using those details to assess audio quality or response speed.

Billing

GPT-Live 1 is billed by call duration at $0.05 per minute, including silence, plus tokens for the backend that handles tools. Standard speech-to-text is not charged on that path.

See the generated API reference for the exact request and response shapes.