# xAI TTS v1 — Text to Speech

**Developer:** xAI  
**Model ID:** `xai/tts-v1`  
**Release Date:** April 2026

## Overview

xAI TTS v1 is a high-fidelity text-to-speech model developed by xAI, the company behind Grok. It converts text into natural, expressive speech with sub-second latency, supporting 20 languages and a rich voice library of 80+ voices. The model features fine-grained delivery control through inline speech tags, multiple audio output formats for both streaming and telephony use cases, and a voice cloning capability that can produce a production-ready custom voice from roughly a minute of reference audio.

xAI TTS v1 is designed for real-world production workloads — customer service bots, content narration, accessibility tools, and real-time voice agents — offering competitive per-character pricing with enterprise-grade compliance.

## Key Capabilities

- **Expressive delivery control** — 14 instant speech tags and 13 wrapping style tags for pauses, laughter, whispers, pitch shifts, speed changes, and more.
- **80+ voices across 20 languages** — Five universal multilingual voices plus language-optimized voices for Chinese, Russian, Italian, French, Spanish, Hindi, Japanese, Korean, Portuguese, German, Dutch, Polish, Turkish, Arabic, Vietnamese, Thai, Danish, Swedish, Finnish, and English.
- **Flexible audio output** — MP3, WAV, PCM, μ-law, and A-law codecs with sample rates from 8 kHz (telephony) to 48 kHz (studio).
- **Voice cloning** — Record up to 120 seconds of reference audio; a custom `voice_id` is ready in under 2 minutes at no additional cost.
- **Streaming and batch modes** — Both a standard REST endpoint and a WebSocket streaming endpoint for real-time audio delivery.
- **Automatic language detection** — Set `language: "auto"` to let the model identify the input language.
- **Privacy-first** — Audio is never stored or used for model training.

## Use Cases

- **Customer service / IVR** — Low-latency telephony output (μ-law/A-law at 8 kHz) for automated voice response systems.
- **Content narration** — Podcast episodes, audiobooks, and video voiceovers with expressive, human-like delivery.
- **Accessibility** — Real-time screen readers and reading assistants for visually impaired users.
- **Real-time voice agents** — Paired with xAI's Speech-to-Text and Voice Agent APIs for end-to-end conversational AI.
- **Multilingual applications** — Localized content delivery across 20 languages from a single API.
- **Custom brand voices** — Clone a spokesperson's voice to maintain consistent audio identity at scale.

## Voices

### Multilingual Voices

These five voices support all 20 available languages.

| Voice ID | Name | Gender | Character |
|----------|------|--------|-----------|
| `eve` | Eve | Female | Energetic, upbeat — default voice |
| `ara` | Ara | Female | Warm and conversational |
| `leo` | Leo | Male | Authoritative, instructional |
| `rex` | Rex | Male | Professional, business tone |
| `sal` | Sal | Male | Versatile, neutral |

### Language-Optimized Voices (selected)

Language-specific voices are optimized for their native language and automatically lock the `language` field when selected.

| Language | Voices |
|----------|--------|
| English | Grace (F), Claire (F), James (M), Daniel (M) |
| Chinese (Mandarin) | Jian (M), Hao (F), Xia (F) |
| Russian | Pavel (M), Andrei (M), Dmitri (M), Irina (F) |
| French | Remi (M), Hugo (M), Camille (F) |
| Spanish | Manuel (M), Javier (M), Diego (M), Andres (M) |
| Italian | Enzo (M), Matteo (M), Alessandro (M), Luca (F) |
| German | Moritz (M), Niklas (M), Clara (F), Lena (F) |
| Japanese | Ren (M), Sakura (F) |
| Korean | Jun-seo (M), Min-jun (M), Seo-yeon (F), Ji-yeon (F) |
| Portuguese | Mateus (M), Rafael (M), Beatriz (F) |
| Hindi | Karan (M), Ananya (F) |
| Arabic | Khalid (M), Tariq (M), Layla (F) |
| Turkish | Emre (M), Kaan (M), Aylin (F) |
| Dutch | Thijs (M), Ruben (M), Femke (F), Noor (F) |
| Polish | Mateusz (M), Jakub (M), Katarzyna (F), Aleksandra (F) |
| Vietnamese | Duc (M), Minh (M), Mai (F) |
| Swedish | Axel (M), Erik (M), Saga (F) |
| Finnish | Valtteri (M), Eero (M), Helmi (F), Elina (F) |
| Thai | Krit (M), Aroon (M) |
| Danish | Lars (M), Kasper (M), Ida (F) |

> The complete voice library, including custom cloned voices, is accessible via the `voice_id` parameter.

## Supported Languages

| Code | Language |
|------|----------|
| `auto` | Auto Detect |
| `en` | English |
| `zh` | Chinese (Mandarin) |
| `ar-EG` | Arabic (Egypt) |
| `ar-SA` | Arabic (Saudi Arabia) |
| `ar-AE` | Arabic (UAE) |
| `bn` | Bengali |
| `fr` | French |
| `de` | German |
| `hi` | Hindi |
| `id` | Indonesian |
| `it` | Italian |
| `ja` | Japanese |
| `ko` | Korean |
| `pt-BR` | Portuguese (Brazil) |
| `pt-PT` | Portuguese (Portugal) |
| `ru` | Russian |
| `es-MX` | Spanish (Mexico) |
| `es-ES` | Spanish (Spain) |
| `tr` | Turkish |
| `vi` | Vietnamese |

## Input Parameters

| Parameter | Type | Default | Description |
|-----------|------|---------|-------------|
| `model` | string | `xai/tts-v1` | Model identifier. Required. |
| `text` | string | — | Text to synthesize. Maximum 15,000 characters. Supports inline speech tags. Required. |
| `language` | string | `auto` | BCP-47 language code or `"auto"` for automatic detection. Required. |
| `voice_id` | string | `eve` | Voice identifier. Multilingual voices support all languages; language-optimized voices lock to their native language. |
| `codec` | string | `mp3` | Output audio codec: `mp3`, `wav`, `pcm`, `mulaw`, `alaw`. |
| `sample_rate` | integer | `24000` | Sample rate in Hz. Options: `8000`, `16000`, `22050`, `24000`, `44100`, `48000`. |
| `bit_rate` | integer | `128000` | Bit rate in bps. MP3 only. Options: `32000`, `64000`, `96000`, `128000`, `192000`. |
| `speed` | number | `1.0` | Playback speed multiplier. Range: `0.7` (slower) to `1.5` (faster). |
| `text_normalization` | boolean | `false` | When `true`, converts written-form text (numbers, abbreviations, symbols) to spoken form before synthesis. |
| `optimize_streaming_latency` | integer | `0` | Streaming latency trade-off: `0` = best quality, `1` = lower first-chunk latency, `2` = lowest first-chunk latency. |

### Audio Format Recommendations

| Use Case | Codec | Sample Rate | Bit Rate |
|----------|-------|-------------|----------|
| Standard playback (default) | `mp3` | 24,000 Hz | 128,000 bps |
| Studio / high-fidelity | `mp3` or `wav` | 44,100 or 48,000 Hz | 192,000 bps |
| Telephony / IVR | `mulaw` or `alaw` | 8,000 Hz | — |
| Streaming (web) | `mp3` | 22,050 Hz | 64,000 bps |

## Inline Speech Tags

Speech tags let you control delivery at a granular level within the `text` field.

### Instant Tags

Insert at any point in the text to trigger an immediate vocal event.

| Tag | Effect |
|-----|--------|
| `[pause]` | Brief pause |
| `[long-pause]` | Extended pause |
| `[hum-tune]` | Soft humming sound |
| `[laugh]` | Full laugh |
| `[chuckle]` | Short chuckle |
| `[giggle]` | Light giggle |
| `[cry]` | Crying sound |
| `[tsk]` | Disapproving tsk |
| `[tongue-click]` | Tongue click |
| `[lip-smack]` | Lip-smack sound |
| `[breath]` | Audible breath |
| `[inhale]` | Inhalation |
| `[exhale]` | Exhalation |
| `[sigh]` | Sigh |

### Wrapping Style Tags

Wrap text to apply a delivery style to the enclosed span.

| Tag | Effect |
|-----|--------|
| `<soft>…</soft>` | Softer, quieter delivery |
| `<whisper>…</whisper>` | Whispered speech |
| `<loud>…</loud>` | Louder, more projected delivery |
| `<build-intensity>…</build-intensity>` | Gradually increasing intensity |
| `<decrease-intensity>…</decrease-intensity>` | Gradually decreasing intensity |
| `<higher-pitch>…</higher-pitch>` | Raised pitch |
| `<lower-pitch>…</lower-pitch>` | Lowered pitch |
| `<slow>…</slow>` | Slower delivery |
| `<fast>…</fast>` | Faster delivery |
| `<sing-song>…</sing-song>` | Melodic, sing-song pattern |
| `<singing>…</singing>` | Full singing mode |
| `<laugh-speak>…</laugh-speak>` | Spoken with laughter mixed in |
| `<emphasis>…</emphasis>` | Stressed emphasis on words |

**Example:**

```
"Welcome back! [pause] <whisper>Just between us</whisper>, the sale ends tonight. [laugh] Don't miss it!"
```

## Rate Limits

| Limit | Value |
|-------|-------|
| Requests per minute (RPM) | 3,000 |
| Requests per second (RPS) | 50 |
| Concurrent sessions per team | 100 |
| Maximum characters per request | 15,000 |

## Pricing

Pricing is based on the number of characters in the input `text` field.

### SKU

| SKU | Description | Unit Price |
|-----|-------------|------------|
| `sku_per_1k_chars` | Per 1,000 characters synthesized | $0.015 |

### Formula

```
cost = countChars(text) / 1000 × sku_per_1k_chars
```

Where `countChars(text)` counts the total number of characters in the input text (including spaces and punctuation, excluding inline speech tags consumed by the model).

The effective rate is **$15.00 per 1,000,000 characters**.

### Examples

| Input Length | Characters | Cost |
|--------------|-----------|------|
| Short sentence | 100 chars | $0.0015 |
| One paragraph | 500 chars | $0.0075 |
| Article excerpt | 2,000 chars | $0.0300 |
| Maximum single request | 15,000 chars | $0.2250 |

> Custom cloned voices are billed at the same per-character rate as built-in voices — there is no additional charge for using a `voice_id` from the Voice Library.

## Enterprise Features

- **SOC 2 Type II** certified
- **HIPAA** eligibility with Business Associate Agreement (BAA)
- **GDPR** compliance with data residency options
- **SAML SSO** and role-based access control (RBAC)
- **Multi-region infrastructure** with custom SLAs available
- **No data retention** — audio is never stored or used for model training

## References

- [xAI Voice Overview](https://docs.x.ai/developers/model-capabilities/audio/voice)
- [Text to Speech API Docs](https://docs.x.ai/developers/models/text-to-speech)
- [Custom Voices Guide](https://docs.x.ai/developers/model-capabilities/audio/custom-voices)
- [xAI TTS & STT Launch Announcement](https://x.ai/news/grok-stt-and-tts-apis)