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VOICE API

Conversation Relay

You handle the text, we handle the media. Conversation Relay streams transcribed voice as text over WebSockets, so you can plug live voice into the AI engine you already run, no audio handling required. Telnyx manages transport, STT, and TTS.

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Conversation Relay
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WHY TELNYX

Best-of-breed speech, on a network built for voice

You bring the intelligence. Telnyx brings the speech layer and the line underneath it.

  • Best-of-breed STT and TTS

    Best-of-breed STT and TTS

    Choose from a range of speech-to-text engines and a catalog of voices. Pick the voice and the accuracy your use case needs, not whatever one vendor ships.

  • Low-latency media

    Low-latency media

    STT and TTS run close to the call, so the audio layer stays fast and the conversation feels natural. Your engine's response time is yours; the media around it is ours.

  • Global reach

    Global reach

    Full programmatic control over PSTN voice services in 140+ countries. Your voice runs on Telnyx's own carrier network, not a resold one. As a licensed carrier, we deliver secure, compliant, and reliable infrastructure.

DEMO

Configure the environment your agents run in

Try different STT, TTS engines and connect a phone number to your agent

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HOW IT WORKS

You own the logic. We own the line.

Telnyx transcribes the caller, streams you the text, and speaks your reply back. Your side of the connection is text from start to finish.

THE DIVISION OF LABOR

You keep full control of how your agent thinks and responds. Everything from the phone number to the spoken word is on us. Here is the exact split.

In your stack

You handle

  • Your LLM and reasoning
  • Your knowledge base
  • Your tools and function calling
  • Your conversation logic

On our network

Telnyx handles

  • Phone numbers and carrier network
  • Voice transport
  • Real-time speech-to-text
  • Text-to-speech and voices
  • DTMF, interruption, and call control

One WebSocket between Telnyx and your application

A single bidirectional connection per session carries the whole exchange as text frames. Open it from TeXML or the Voice API, point it at your endpoint, and you are live.

Explore dev docs

TeXML

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Connect>
    <ConversationRelay
      url="wss://yourdomain.com/conversation-relay"
      voice="Telnyx.Ultra.01eaafa9-308a-4276-a017-6ab0cf061b1f"
      language="en"
      transcriptionProvider="deepgram"
      welcomeGreeting="Welcome! How can I help you today?"
    />
  </Connect>
</Response>

Voice API

curl -X POST https://api.telnyx.com/v2/calls/{call_control_id}/actions/conversation_relay_start \
  --header "Content-Type: application/json" \
  --header "Authorization: Bearer ***" \
  --data '{
    "url": "wss://yourdomain.com/conversation-relay",
    "voice": "Telnyx.Ultra.01eaafa9-308a-4276-a017-6ab0cf061b1f",
    "language": "en-US",
    "transcription_engine": "Deepgram",
    "greeting": "Welcome! How can I help you today?"
  }'

TeXML multi-language

<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Connect>
    <ConversationRelay
      url="wss://yourdomain.com/conversation-relay"
      voice="Telnyx.Ultra.01eaafa9-308a-4276-a017-6ab0cf061b1f"
      language="en"
      transcriptionProvider="deepgram"
      welcomeGreeting="Press 1 for English, 2 for French, 3 for Spanish."
      dtmfDetection="true"
    >
      <Language code="fr" voice="Telnyx.Ultra.0d09e991-5763-406e-b637-02bc431ef72d" transcriptionProvider="google" />
      <Language code="es" voice="Telnyx.Ultra.13ff5deb-2591-42ad-a356-63a04e524411" transcriptionProvider="telnyx" />
    </ConversationRelay>
  </Connect>
</Response>

WebSocket

// Telnyx sends the caller's speech as text
{ "type": "prompt", "voicePrompt": "what are your hours", "lang": "en", "last": true }

// Your app sends text back to speak
{ "type": "text", "token": "We're …day.", "last": true }
PRICING

Transparent pricing, pay for what you use

Starting at $0.05 per minute. You bring your own AI engine, so there is no model or platform fee from Telnyx for the reasoning layer.

$0.05

Starting cost per minute

See pricing
PRODUCTS

The rest of the stack, when you want it

Conversation Relay is one way in. When you are ready for Telnyx to run the model too, the Voice AI Platform, Inference, Speech to Text, and Text to Speech all sit on the same network, same API key, same bill.

See all products
  • Text to Speech

    Text to Speech

    One API for leading voice engines. Access a catalog of natural and HD voices without lock-in.

    Learn more
  • Speech to Text

    Speech to Text

    Real-time transcription with best-of-breed engines. Choose accuracy, speed, and vendor for your use case.

    Learn more

  • Voice AI Platform

    Build and deploy low-latency Voice AI agents in minutes on a full-stack, conversational AI platform.

    Learn more
  • Inference

    Inference

    Serverless inference on GPUs Telnyx owns. Run open-source and frontier models on the same network, API key, and bill.

    Learn more
  • Deepfake Detection

    Deepfake Detection

    Detect AI-generated voice fraud in real time, built into the Telnyx voice network.

    Learn more

Sign up and start building

Keep your AI engine. Add voice without the audio pipeline.

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FAQ

Conversation Relay connects a live Telnyx call to your WebSocket application. Telnyx handles speech recognition and text-to-speech; your application receives the caller's words as text and sends text back to be spoken. It lets you add voice to a text-based AI workflow without processing raw audio.