In-Call Playback

In-call TTS plays synthesized speech during live voice calls. Two integration paths:

Voice API

Use the speak command to play TTS on an active call:

curl --location 'https://api.telnyx.com/v2/calls/{call_control_id}/actions/speak' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer YOUR_API_KEY' \
--data '{
  "voice": "Telnyx.Ultra.3e1ed423-17e5-4773-b87c-25b031106e41"
}'

See Voice API docs for the full command reference.

TeXML

Use the <Say> element:

<Response>
  <Say voice="Telnyx.Ultra.Clara">Your appointment is confirmed for tomorrow at 3 PM.</Say>
</Response>

See TeXML docs for the full <Say> reference.

AI Assistants

AI Assistants use TTS for voice output. Configure the voice model in assistant settings. See AI Assistants for voice configuration.

Voice Selection

In-call TTS uses the same voice format as WebSocket and REST:

Provider.Model.VoiceId

All models (including Ultra) are available for in-call playback.

WebSocket Streaming

REST API

Providers

Other

API Reference

For AI Agents

In-Call Playback

Voice API

TeXML

AI Assistants

Voice Selection

​Voice API

​TeXML

​AI Assistants

​Voice Selection

Voice API

TeXML

AI Assistants

Voice Selection