# OpenRouter APIs — Google: Gemini 3.1 Flash TTS Preview (google/gemini-3.1-flash-tts-preview)

Guide for calling every confirmed OpenRouter API that serves `google/gemini-3.1-flash-tts-preview`.

Model page: https://openrouter.ai/google/gemini-3.1-flash-tts-preview
Create an API key: https://openrouter.ai/settings/keys

## Authentication

Send this header with every request:

- Authorization: Bearer $OPENROUTER_API_KEY

## Text-to-Speech API

Synthesize audio with `google/gemini-3.1-flash-tts-preview` through OpenRouter's Text-to-Speech API.

Docs: https://openrouter.ai/docs/api/api-reference/tts/create-speech

### Endpoint

POST https://openrouter.ai/api/v1/audio/speech

Headers:
- Content-Type: application/json

### Request fields (google/gemini-3.1-flash-tts-preview)

- model: string (required) — `"google/gemini-3.1-flash-tts-preview"`
- input: string (required) — text to synthesize
- voice: "Zephyr" | "Puck" | "Charon" | "Kore" | "Fenrir" | "Leda" | "Orus" | "Aoede" | "Callirrhoe" | "Autonoe" | "Enceladus" | "Iapetus" | "Umbriel" | "Algieba" | "Despina" | "Erinome" | "Algenib" | "Rasalgethi" | "Laomedeia" | "Achernar" | "Alnilam" | "Schedar" | "Gacrux" | "Pulcherrima" | "Achird" | "Zubenelgenubi" | "Vindemiatrix" | "Sadachbia" | "Sadaltager" | "Sulafat" (optional) — provider-specific voice identifier
- response_format: "mp3" | "pcm" (optional) — output audio encoding; defaults to pcm

### Response

Success returns raw audio bytes, not JSON.

- `Content-Type` identifies the audio encoding, such as `audio/mpeg` or `audio/pcm`.
- `X-Generation-Id` identifies the billed generation.
- Write the response body directly to an audio file; do not call `response.json()`.

### Examples

#### Text to Speech

```bash
curl https://openrouter.ai/api/v1/audio/speech \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  --output output.pcm \
  -d '{
  "model": "google/gemini-3.1-flash-tts-preview",
  "input": "[calm] The warm light flows across the OpenRouter office as the evening settles in and the routing never stops. One interface, hundreds of models. Ready when you are.",
  "voice": "Orus",
  "response_format": "pcm"
}'
```

#### Text to Speech 2

```bash
curl https://openrouter.ai/api/v1/audio/speech \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  --output output.pcm \
  -d '{
  "model": "google/gemini-3.1-flash-tts-preview",
  "input": "[calm and dramatic] The warm light flows across the OpenRouter office as the evening settles in and the routing never stops. One interface, hundreds of models. Ready when you are.",
  "voice": "Orus",
  "response_format": "pcm"
}'
```

### Error differences

- 400 — malformed audio input or an audio option the routed provider does not support
- 502 — the upstream audio operation failed

## Errors

Failures return `{"error": {"code": <number>, "message": <string>}}` with the HTTP status:

- 400 — malformed request or an unsupported parameter
- 401 — missing or invalid API key
- 402 — insufficient credits
- 403 — spend limit reached, key disabled, or access blocked
- 404 — unknown model or no provider can serve the request
- 429 — rate limited; retry with backoff
- 502 — the operation failed upstream; failed generations are not billed

---

Canonical version of this document: https://openrouter.ai/google/gemini-3.1-flash-tts-preview/llms.txt