> ## Documentation Index
> Fetch the complete documentation index at: https://docs.runflow.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Gemini TTS

> Google's Gemini TTS converts text to realistic audio. 30 voice presets, multi-speaker synthesis (up to 10 speakers), 24+ languages, and inline style markers for expressive control.

<Info>
  Pricing: **\$10/1m-tokens**. Endpoint: `POST /v1/models/google/gemini-tts/runs`.
</Info>

Google's Gemini TTS converts text to realistic audio. 30 voice presets, multi-speaker synthesis (up to 10 speakers), 24+ languages, and inline style markers for expressive control.

## Overview

* **Endpoint**: [https://api.runflow.io/v1/models/google/gemini-tts/runs](https://api.runflow.io/v1/models/google/gemini-tts/runs)
* **Model ID**: google/gemini-tts
* **Provider**: Google
* **License**: commercial
* **Last Updated**: 2026-04-08

## Pricing

* **Base price**: \$10/1m-tokens
* **Note**: Per 1M tokens (flash, output-dominated)

# Gemini TTS API

**Endpoint:** `POST /v1/models/google/gemini-tts/runs`

## Run the model

### Python

```python theme={"dark"}
import requests

response = requests.post(
    "https://api.runflow.io/v1/models/google/gemini-tts/runs",
    headers={"Authorization": "Bearer RUNFLOW_API_KEY"},
    json={
        "input": {},
        "callback_url": "https://your-server.com/webhook"
    },
)

data = response.json()
print(data)
```

### Node.js

```javascript theme={"dark"}
const response = await fetch(
  "https://api.runflow.io/v1/models/google/gemini-tts/runs",
  {
    method: "POST",
    headers: {
      "Authorization": "Bearer RUNFLOW_API_KEY",
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
        "input": {},
        "callback_url": "https://your-server.com/webhook"
    }),
  }
);

const data = await response.json();
console.log(data);
```

### cURL

```bash theme={"dark"}
curl -X POST https://api.runflow.io/v1/models/google/gemini-tts/runs \
  -H "Authorization: Bearer $RUNFLOW_API_KEY" \
  -H "Content-Type: application/json" \
  --data-binary @- <<'JSON'
{
    "input": {},
    "callback_url": "https://your-server.com/webhook"
}
JSON
```

## Request parameters

| Parameter      | Type           | Required | Description                                                 |
| -------------- | -------------- | -------- | ----------------------------------------------------------- |
| `input`        | object         | required | Model input parameters. See "Input schema" below.           |
| `callback_url` | string \| null | optional | Webhook URL - POSTed when the run reaches a terminal state. |
| `metadata`     | object \| null | optional | Arbitrary key-value pairs attached to the run.              |

## Input schema

| Field                | Type   | Required | Allowed values                                                                                                                                                                                                                                                                                                                                       | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| -------------------- | ------ | -------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `prompt`             | string | required | Any                                                                                                                                                                                                                                                                                                                                                  | The text to convert to speech. Gemini TTS supports natural-language prompting for style, pace, accent, and emotional expression - include delivery instructions inline with the text (e.g. 'Say cheerfully: Have a wonderful day!'). For multi-speaker synthesis, prefix lines with speaker aliases defined in the speakers field (e.g. 'Alice: Hello!\nBob: Hi!'). Supports inline pace/style markers like \[slowly], \[whispering], \[excited], \[extremely fast]. |
| `speakers`           | json   | optional | Any                                                                                                                                                                                                                                                                                                                                                  | Multi-speaker voice configuration. When set, enables multi-speaker synthesis where different parts of the text are spoken by different voices. Each speaker needs a voice and a speaker\_id (alias) that matches prefixes in the prompt. Requires gemini-2.5-pro-tts or gemini-2.5-flash-tts model. Not supported with gemini-2.5-flash-lite-preview-tts.                                                                                                            |
| `output_format`      | string | optional | `wav`, `mp3`, `ogg_opus`                                                                                                                                                                                                                                                                                                                             | Audio output format. mp3: compressed, small file size (recommended). wav: uncompressed PCM wrapped in WAV (24 kHz, 16-bit mono). ogg\_opus: Ogg container with Opus codec, good quality-to-size ratio.                                                                                                                                                                                                                                                               |
| `model`              | string | optional | `gemini-2.5-flash-tts`, `gemini-2.5-pro-tts`                                                                                                                                                                                                                                                                                                         | Which Gemini TTS model to use. gemini-2.5-flash-tts: low latency, cost-efficient for everyday applications (recommended). gemini-2.5-pro-tts: highest quality, best for structured workflows like podcasts, audiobooks, and customer support.                                                                                                                                                                                                                        |
| `voice`              | string | optional | `Achernar`, `Achird`, `Algenib`, `Algieba`, `Alnilam`, `Aoede`, `Autonoe`, `Callirrhoe`, `Charon`, `Despina`, `Enceladus`, `Erinome`, `Fenrir`, `Gacrux`, `Iapetus`, `Kore`, `Laomedeia`, `Leda`, `Orus`, `Pulcherrima`, `Puck`, `Rasalgethi`, `Sadachbia`, `Sadaltager`, `Schedar`, `Sulafat`, `Umbriel`, `Vindemiatrix`, `Zephyr`, `Zubenelgenubi` | Voice preset for single-speaker synthesis. 30 distinct voices are available. Ignored when speakers is set. Popular choices: Kore (strong, firm female), Puck (upbeat, lively male), Charon (calm, professional male), Zephyr (bright, clear female), Aoede (warm, melodic female).                                                                                                                                                                                   |
| `language_code`      | string | optional | Any                                                                                                                                                                                                                                                                                                                                                  | Language for multilingual synthesis. When set, steers the model to speak in the specified language. Supports 24 GA languages and 60+ Preview languages. If not set, the model auto-detects the language from the text.                                                                                                                                                                                                                                               |
| `temperature`        | float  | optional | Any                                                                                                                                                                                                                                                                                                                                                  | Controls the randomness of the speech output. Higher values produce more creative and varied delivery, while lower values make the output more predictable and focused.                                                                                                                                                                                                                                                                                              |
| `style_instructions` | string | optional | Any                                                                                                                                                                                                                                                                                                                                                  | Optional style and delivery instructions prepended to the prompt. Controls expressiveness, accent, pace, tone, and emotional expression using natural language. Use this to separate style control from the text content. Examples: 'Speak warmly and slowly', 'Read this as a dramatic newscast', 'Use a British accent with a cheerful tone', 'Whisper mysteriously'.                                                                                              |

## Output schema

| Field           | Type | Description                                                                                      |
| --------------- | ---- | ------------------------------------------------------------------------------------------------ |
| `outputs`       | json | Unified output array - one entry per generated artifact with url/type/width/height/duration/etc. |
| `nsfw_detected` | json | true if the provider flagged output as NSFW, false if cleared, null if not checked.              |
| `seed`          | json | Deterministic seed used for generation, or null if the provider doesn't return one.              |
| `timing`        | json | Provider timing info (inference\_ms etc.), or null.                                              |

## Callback payload

When you provide a `callback_url`, Runflow POSTs to it once the run reaches a terminal state.

| Field          | Type           | Description                                                    |
| -------------- | -------------- | -------------------------------------------------------------- |
| `event`        | string         | Event type: "run.completed", "run.failed", or "run.cancelled". |
| `run_id`       | string         | The unique identifier of the run.                              |
| `status`       | string         | Terminal status: "succeeded", "failed", or "cancelled".        |
| `output`       | object \| null | The run output. Null if the run failed or was cancelled.       |
| `duration_ms`  | number \| null | Total run duration in milliseconds.                            |
| `created_at`   | string \| null | ISO 8601 timestamp when the run was created.                   |
| `completed_at` | string \| null | ISO 8601 timestamp when the run reached terminal state.        |
| `metadata`     | object \| null | The metadata object passed at run creation, if any.            |

* **Retries:** 3 attempts with exponential backoff (1s, 2s). Retries on 5xx / network errors only.
* **Headers:** `Runflow-Request-Id` is always sent. `Runflow-Signature` is sent if a signing secret is configured.

## Additional Resources

* [Playground](https://app.runflow.io/models/google/gemini-tts)
* [API Reference](https://app.runflow.io/models/google/gemini-tts?tab=api)
* [Documentation](https://docs.runflow.io)
* [OpenAPI](https://docs.runflow.io/api/openapi.public.json)

## Related

<CardGroup cols={2}>
  <Card title="Browse all models" icon="grid" href="/models">Browse the catalog.</Card>
  <Card title="Run lifecycle" icon="play" href="/concepts/runs">Callbacks, polling, statuses.</Card>
  <Card title="Callbacks" icon="webhook" href="/concepts/callbacks">Handle async results.</Card>
  <Card title="Pricing" icon="coin" href="/concepts/pricing">How requests bill out.</Card>
</CardGroup>