OpenAI Compatibility

Realtime TTS serves OpenAI's text-to-speech endpoint, POST /v1/audio/speech, in OpenAI's own request and response format. If your app already uses OpenAI's text-to-speech, point the SDK at Inworld with your Inworld API key, then set model and voice to Inworld IDs. The SDK calls themselves stay the same.

Endpoint

https://api.inworld.ai/v1

Change your SDK base URL from https://api.openai.com/v1 to https://api.inworld.ai/v1. In the US region, the same base URL also serves the Inworld Router, so one client configuration covers both LLM and TTS.

For regional deployments, use https://api.eu.inworld.ai/v1 or https://api.in.inworld.ai/v1 with an API key created in that region's Portal. Regional endpoints are provisioned per organization on Enterprise plans, and keys from the US region do not authenticate against them. The Inworld Router is not available in regional deployments.

Quickstart

Use your Inworld API key as the SDK's API key. The OpenAI SDKs send it as Authorization: Bearer <key>; the endpoint also accepts Authorization: Basic <key>. Keep the key on your server.

from openai import OpenAI

client = OpenAI(
    base_url="https://api.inworld.ai/v1",
    api_key="YOUR_INWORLD_API_KEY",
)

with client.audio.speech.with_streaming_response.create(
    model="inworld-tts-2",
    voice="Dennis",
    input="Welcome back! Your order shipped this morning and should arrive by Thursday.",
) as response:
    response.stream_to_file("speech.mp3")

import fs from 'node:fs';
import OpenAI from 'openai';

const client = new OpenAI({
  baseURL: 'https://api.inworld.ai/v1',
  apiKey: 'YOUR_INWORLD_API_KEY',
});

const response = await client.audio.speech.create({
  model: 'inworld-tts-2',
  voice: 'Dennis',
  input: 'Welcome back! Your order shipped this morning and should arrive by Thursday.',
});

fs.writeFileSync('speech.mp3', Buffer.from(await response.arrayBuffer()));

curl -X POST https://api.inworld.ai/v1/audio/speech \
  -H "Authorization: Basic $INWORLD_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "inworld-tts-2",
    "voice": "Dennis",
    "input": "Welcome back! Your order shipped this morning and should arrive by Thursday."
  }' \
  --output speech.mp3

Request parameters

The API reference has the full request and response schema.

The language is detected from the input text.

Audio formats

All formats are mono.

Streaming

With the default stream_format, audio bytes arrive as they are generated, so you can play them before synthesis finishes. Read the response incrementally instead of waiting for the whole body — for example with with_streaming_response in Python, or by reading response.body in Node.

With stream_format set to sse, the response is a stream of server-sent events. Each speech.audio.delta event carries a base64-encoded audio chunk in audio, and the stream ends with a speech.audio.done event:

data: {"type":"speech.audio.delta","audio":"SUQzBAAAAAAAI1RTU0UAAAAPAAAD..."}

data: {"type":"speech.audio.done"}

Errors

Errors use OpenAI's error format, so the OpenAI SDKs raise their usual exception types:

{
  "error": {
    "message": "speed must be between 0.5 and 1.5",
    "type": "invalid_request_error",
    "param": "speed",
    "code": null
  }
}

Billing and limits

Requests are billed per character and share rate limits and concurrency limits with the Streaming API.

Features that need the native API

The OpenAI format has no fields for some Realtime TTS features. Use the native TTS API for:

• Timestamps for captions and lipsync
• Sample rate, bit rate, and other audio encoding settings
• Synthesis context from earlier conversation turns
• Explicit language selection, delivery mode, temperature, and text normalization settings
• Async and batch jobs