How do I use the Rex voice in the xAI API?

Send a POST request to https://api.x.ai/v1/tts with "voice_id": "rex" in the JSON body, along with the text and a language code (or "auto"). The response is the audio file. The same id works as the voice of a Grok Voice 3.0 speech-to-speech session.

Can Rex speak languages other than English?

Yes. Every built-in Grok voice, Rex included, speaks all 20 languages the API validates, from Chinese and Japanese to Hindi, Arabic, Spanish and Portuguese. Pick the language above or leave it on auto-detect.

Is the Rex voice free to use?

Trying Rex here is free, up to 1,000 characters per request. In your own app, xAI bills $15 per million characters for text to speech, whichever built-in voice you choose.

Grok Rex Voice: Free Rex Text to Speech Online

Hear the Grok Rex voice with your own text and download it as MP3. Rex is one of the 28 built-in xAI Grok voices (voice_id "rex"), speaks 20 languages and supports speech tags.

Voice

RexChange voice

Text to speak

114 / 1,000 characters

Add expression

More tags

Click to insert at the cursor. Inline tags like [pause] go where the sound happens; wrapping tags like <whisper> go around a phrase.

Your text goes through our server to xAI's Grok speech model to make the audio, then is discarded. Privacy Policy

About the Rex voice

One of the original Grok voices; xAI uses Rex in its own high-fidelity MP3 example in the API docs.

Rex is one of the five original Grok voices, so it is the same voice you hear in the Grok app's voice mode. We suggest trying it first for ads, trailers, sports, but every Grok voice handles every kind of text; the samples above let you judge in seconds.

Use Rex in the xAI text to speech API

The voice id is rex (case-insensitive). A complete request:

curl -X POST https://api.x.ai/v1/tts \
  -H "Authorization: Bearer $XAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "text": "Hello, this is Rex. [pause] Nice to meet you.",
    "voice_id": "rex",
    "language": "en",
    "speed": 1.0
  }' \
  --output rex.mp3

Add output_format for WAV, PCM or telephony codecs, with_timestamps for per-character timing, and the same voice_id as the voice of a Grok voice agent. Full parameter list in the Grok Voice API guide; official reference at docs.x.ai.

Languages Rex can speak

English, Arabic (Egypt), Arabic (Saudi Arabia), Arabic (UAE), Bengali, Chinese (Simplified), French, German, Hindi, Indonesian, Italian, Japanese, Korean, Portuguese (Brazil), Portuguese (Portugal), Russian, Spanish (Mexico), Spanish (Spain), Turkish, Vietnamese. Pass the BCP-47 code (for example zh, ja, pt-BR) or auto.

Compare with the original Grok voices

Grok Ara voice — narration, product demos
Grok Eve voice — announcements, explainer videos
Grok Leo voice — documentaries, audiobooks
Grok Sal voice — podcasts, radio-style reads

All 28 Grok voices

As of October 2026, xAI’s docs list 28 built-in voices (checked 17 Oct 2026). Every one speaks all 20 supported languages. Open a voice to try it with your own text.