Ultra

Telnyx Ultra — sub-100ms latency, 44 languages, REST only.

Voice format: Telnyx.Ultra.<voice>

Sub-100ms latency. 36 languages.

REST only — Ultra is not available over public WebSocket.

Voice Samples

Voice	Language	Gender	Sample
Telnyx.Ultra.Asher	en	Male
Telnyx.Ultra.Callie	en	Female
Telnyx.Ultra.Clara	en-US	Female

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SSML Emotions

Ultra supports inline SSML emotion tags. Place the tag before the text:

<emotion value="excited" />Great news — your order shipped early!

Primary emotions: angry, excited, content, sad, scared.

Additional: happy, enthusiastic, curious, calm, grateful, affectionate, sarcastic, surprised, confident, hesitant, apologetic, determined, frustrated, disappointed.

Omitting the tag = neutral delivery. Use sparingly — Ultra interprets emotional subtext from the text itself.

Nonverbal Cues

Insert [laughter] inline for natural laughing:

That's hilarious! [laughter] Anyway, let me check your account.

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Language Support

Set language_boost to improve pronunciation for the target language:

Arabic, Bengali, Bulgarian, Chinese, Czech, Danish, Dutch, English, Finnish, French, German, Gujarati, Hebrew, Hindi, Indonesian, Italian, Japanese, Korean, Malay, Marathi, Māori, Norwegian, Polish, Portuguese, Punjabi, Romanian, Russian, Slovak, Spanish, Swedish, Tamil, Telugu, Thai, Turkish, Ukrainian, Vietnamese.

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REST API

Fields

Field	Type	Default	Description
voice_speed	float	1.0	Speech rate multiplier.
language_boost	string	—	Target language hint.
volume	float	—	Output volume.
emotion	string	—	neutral, happy, sad, angry, fearful, disgusted, surprised.
sampling_rate	integer	—	Output sample rate in Hz.
output_type	string	binary_output	binary_output, base64_output, or audio_id.

Response

Default (binary_output): chunked audio bytes with Content-Type: audio/mpeg.

With output_type: "base64_output": JSON with base64-encoded audio.

With output_type: "audio_id": JSON with an audio_url for deferred retrieval.

See also

xAI Grok is the second TTS provider supporting Expressive Mode. For Grok voice options, see Grok Voices. Note: Grok voices have higher latency than Ultra.