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

# POST /v1/audio/*

> OpenAI-compatible text to speech and transcription through the LangWatch AI Gateway, for OpenAI and ElevenLabs voice models.

OpenAI-compatible audio endpoints. Any client that speaks OpenAI's audio API (the official SDKs, LiveKit and Pipecat voice agents, [Scenario](https://scenario.langwatch.ai)'s voice testing harness) works with zero code change by pointing its `OPENAI_BASE_URL` at the gateway and its `OPENAI_API_KEY` at a LangWatch virtual key. Voice traffic gets the same governance as chat: virtual-key auth, model allowlists, budgets, rate limits, and per-call observability.

Two providers ship today:

| Provider   | TTS (`/v1/audio/speech`)                                                                          | STT (`/v1/audio/transcriptions`)                                                |
| ---------- | ------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------- |
| OpenAI     | `openai/gpt-4o-mini-tts`, `openai/tts-1`, `openai/tts-1-hd`                                       | `openai/gpt-4o-transcribe`, `openai/gpt-4o-mini-transcribe`, `openai/whisper-1` |
| ElevenLabs | `elevenlabs/eleven_flash_v2`, `elevenlabs/eleven_turbo_v2_5`, `elevenlabs/eleven_multilingual_v2` | `elevenlabs/scribe_v1`                                                          |

Configure the provider key once in **Settings → Model Providers** (OpenAI and ElevenLabs both take a plain API key); every virtual key routed to that provider can then call its voice models.

## Text to speech

```
POST /v1/audio/speech
Authorization: Bearer vk-lw-<ULID>
Content-Type: application/json
```

Body matches OpenAI's [speech schema](https://platform.openai.com/docs/api-reference/audio/createSpeech). For ElevenLabs models, put the ElevenLabs **voice id** in the same `voice` field.

```json theme={null}
{
  "model": "elevenlabs/eleven_flash_v2",
  "voice": "cjVigY5qzO86Huf0OWal",
  "input": "Hello! How can I help you today?",
  "response_format": "mp3"
}
```

The response body is the **raw audio bytes** with the matching `Content-Type` (`audio/mpeg`, `audio/wav`, `audio/pcm`, …) with no JSON envelope, exactly like OpenAI, so `client.audio.speech.create(...)` consumes it unchanged. `response_format: "pcm"` returns raw PCM16 for realtime consumers.

```python theme={null}
from openai import OpenAI

client = OpenAI(
    base_url="https://gateway.langwatch.ai/v1",
    api_key="vk-lw-...",
)
audio = client.audio.speech.create(
    model="openai/gpt-4o-mini-tts",
    voice="nova",
    input="Hello from the gateway.",
    response_format="pcm",
)
pcm_bytes = audio.read()
```

## Transcription

```
POST /v1/audio/transcriptions
Authorization: Bearer vk-lw-<ULID>
Content-Type: multipart/form-data
```

Form matches OpenAI's [transcription schema](https://platform.openai.com/docs/api-reference/audio/createTranscription): a `file` part plus `model`, and optionally `language`, `prompt`, `response_format`, `temperature`. Uploads are capped at 25 MB (matching OpenAI's own limit); larger uploads get a `413` before any provider is contacted.

```python theme={null}
transcript = client.audio.transcriptions.create(
    model="elevenlabs/scribe_v1",
    file=open("call-recording.wav", "rb"),
)
print(transcript.text)
```

The response is the standard JSON transcript with `text`, plus whatever the provider reports (duration, segments, token usage).

## Observability and cost measures

Every audio call lands as a gateway trace like chat does. Providers that report token usage (`gpt-4o-mini-tts`, `gpt-4o-transcribe`) fill the standard `gen_ai.usage.*` token attributes; character- and duration-priced providers are measured by two audio-specific attributes:

| Attribute                    | Meaning                                     |
| ---------------------------- | ------------------------------------------- |
| `gen_ai.usage.input_chars`   | Characters synthesized by a TTS call        |
| `gen_ai.usage.audio_seconds` | Seconds of audio transcribed by an STT call |

## Errors

Same error surface as every other endpoint; see [Errors](/docs/ai-gateway/api/errors). Provider rejections (an invalid ElevenLabs voice id, an unsupported format) pass through with the provider's own status code and body. A model outside the virtual key's allowlist returns the standard `model_not_allowed`; a provider with no key configured returns `no_provider_configured`.

## Not yet supported

* **Streaming TTS/STT** (`stream=true`): requests are served complete; streaming is a follow-up.
* **Realtime voice websockets** (OpenAI Realtime, ElevenLabs ConvAI): connect directly to the provider for realtime sessions; the gateway serves the request/response audio endpoints.