---
title: Inworld TTS-1.5 Max | Runware Docs
url: https://runware.ai/docs/models/inworld-tts-1-5-max
description: High-fidelity expressive text-to-speech with rich prosody and multilingual support
---
# Inworld TTS-1.5 Max

Inworld TTS-1.5 Max is a high-fidelity text-to-speech model engineered for expressive voice synthesis with rich prosody, nuanced emotional range, and broadcast-ready audio quality. It supports a wide set of languages and delivers more natural pronunciation and expressive variation suitable for narration, content creation, and immersive character voices. The Max variant prioritizes audio quality and expressiveness while still supporting responsive generation.

- **ID**: `inworld:tts@1.5-max`
- **Status**: live
- **Creator**: Inworld AI
- **Release Date**: January 21, 2026
- **Capabilities**: Text to Audio

## Pricing

$0.05 / 1000 characters

- **1000 characters**: `$0.05`

## Request Parameters

**API Options**

Platform-level options for task execution and delivery.

### [taskType](https://runware.ai/docs/models/inworld-tts-1-5-max#request-tasktype)

- **Type**: `string`
- **Required**: true
- **Value**: `audioInference`

Identifier for the type of task being performed

### [taskUUID](https://runware.ai/docs/models/inworld-tts-1-5-max#request-taskuuid)

- **Type**: `string`
- **Required**: true
- **Format**: `UUID v4`

UUID v4 identifier for tracking tasks and matching async responses. Must be unique per task.

### [outputType](https://runware.ai/docs/models/inworld-tts-1-5-max#request-outputtype)

- **Type**: `string`
- **Default**: `URL`

Audio output type.

**Allowed values**: `URL` `base64Data` `dataURI`

### [outputFormat](https://runware.ai/docs/models/inworld-tts-1-5-max#request-outputformat)

- **Type**: `string`
- **Default**: `MP3`

Specifies the file format of the generated output. The available values depend on the task type and the specific model's capabilities.

- \`MP3\`: Compressed audio, smaller file size.
- \`WAV\`: Uncompressed, high-quality audio.
- \`FLAC\`: Lossless compression.
- \`OGG\`: Open-source compressed audio format (Vorbis codec).

**Allowed values**: `MP3` `WAV` `FLAC` `OGG`

### [webhookURL](https://runware.ai/docs/models/inworld-tts-1-5-max#request-webhookurl)

- **Type**: `string`
- **Format**: `URI`

Specifies a webhook URL where JSON responses will be sent via HTTP POST when generation tasks complete. For batch requests with multiple results, each completed item triggers a separate webhook call as it becomes available.

**Learn more** (1 resource):

- [Webhooks](https://runware.ai/docs/platform/webhooks) (platform)

### [deliveryMethod](https://runware.ai/docs/models/inworld-tts-1-5-max#request-deliverymethod)

- **Type**: `string`
- **Default**: `sync`

Determines how the API delivers task results.

**Allowed values**:

- `sync` Returns complete results directly in the API response.
- `async` Returns an immediate acknowledgment with the task UUID. Poll for results using getResponse.

**Learn more** (1 resource):

- [Task Polling](https://runware.ai/docs/platform/task-polling) (platform)

### [uploadEndpoint](https://runware.ai/docs/models/inworld-tts-1-5-max#request-uploadendpoint)

- **Type**: `string`
- **Format**: `URI`

Specifies a URL where the generated content will be automatically uploaded using the HTTP PUT method. The raw binary data of the media file is sent directly as the request body. For secure uploads to cloud storage, use presigned URLs that include temporary authentication credentials.

**Common use cases:**

- **Cloud storage**: Upload directly to S3 buckets, Google Cloud Storage, or Azure Blob Storage using presigned URLs.
- **CDN integration**: Upload to content delivery networks for immediate distribution.

```text
// S3 presigned URL for secure upload
https://your-bucket.s3.amazonaws.com/generated/content.mp4?X-Amz-Signature=abc123&X-Amz-Expires=3600

// Google Cloud Storage presigned URL
https://storage.googleapis.com/your-bucket/content.jpg?X-Goog-Signature=xyz789

// Custom storage endpoint
https://storage.example.com/uploads/generated-image.jpg
```

The content data will be sent as the request body to the specified URL when generation is complete.

### [ttl](https://runware.ai/docs/models/inworld-tts-1-5-max#request-ttl)

- **Type**: `integer`
- **Min**: `60`

Time-to-live (TTL) in seconds for generated content. Only applies when `outputType` is `URL`.

### [includeCost](https://runware.ai/docs/models/inworld-tts-1-5-max#request-includecost)

- **Type**: `boolean`
- **Default**: `false`

Include task cost in the response.

### [numberResults](https://runware.ai/docs/models/inworld-tts-1-5-max#request-numberresults)

- **Type**: `integer`
- **Min**: `1`
- **Max**: `4`
- **Default**: `1`

Number of results to generate. Each result uses a different seed, producing variations of the same parameters.

**Generation Parameters**

Core parameters for controlling the generated content.

### [audioSettings](https://runware.ai/docs/models/inworld-tts-1-5-max#request-audiosettings)

- **Path**: `audioSettings.bitrate`
- **Type**: `object (3 properties)`

Advanced settings for audio generation.

#### [bitrate](https://runware.ai/docs/models/inworld-tts-1-5-max#request-audiosettings-bitrate)

- **Path**: `audioSettings.bitrate`
- **Type**: `integer`
- **Min**: `1`

Target audio bitrate in kbps. Constraints depend on the output format.

#### [sampleRate](https://runware.ai/docs/models/inworld-tts-1-5-max#request-audiosettings-samplerate)

- **Path**: `audioSettings.sampleRate`
- **Type**: `integer`
- **Min**: `1000`

Audio sample rate in Hz.

#### [channels](https://runware.ai/docs/models/inworld-tts-1-5-max#request-audiosettings-channels)

- **Path**: `audioSettings.channels`
- **Type**: `integer`
- **Default**: `2`

Number of audio channels in the generated output (1 for Mono, 2 for Stereo).

**Allowed values**: `1` `2`

### [model](https://runware.ai/docs/models/inworld-tts-1-5-max#request-model)

- **Type**: `string`
- **Required**: true
- **Value**: `inworld:tts@1.5-max`

Identifier of the model to use for generation.

**Learn more** (3 resources):

- [Text To Image: Model Selection The Foundation Of Generation](https://runware.ai/docs/guides/text-to-image#model-selection-the-foundation-of-generation) (guide)
- [Image Inpainting: Model Specialized Inpainting Models](https://runware.ai/docs/guides/image-inpainting#model-specialized-inpainting-models) (guide)
- [Image Outpainting: Other Critical Parameters](https://runware.ai/docs/guides/image-outpainting#other-critical-parameters) (guide)

### [speech](https://runware.ai/docs/models/inworld-tts-1-5-max#request-speech)

- **Path**: `speech.text`
- **Type**: `object (3 properties)`
- **Required**: true

Settings for speech generation.

#### [text](https://runware.ai/docs/models/inworld-tts-1-5-max#request-speech-text)

- **Path**: `speech.text`
- **Type**: `string`
- **Required**: true
- **Min**: `2`
- **Max**: `2000`

Text to convert to speech.

#### [voice](https://runware.ai/docs/models/inworld-tts-1-5-max#request-speech-voice)

- **Path**: `speech.voice`
- **Type**: `string`
- **Required**: true
- **Default**: `auto`

Voice identifier to use. Set to `auto` for automatic selection.

**Allowed values**: `Loretta` `Darlene` `Marlene` `Hank` `Evelyn` `Celeste` `Pippa` `Tessa` `Liam` `Callum` `Hamish` `Abby` `Graham` `Rupert` `Mortimer` `Snik` `Anjali` `Saanvi` `Arjun` `Claire` `Oliver` `Simon` `Elliot` `James` `Serena` `Gareth` `Vinny` `Lauren` `Jessica` `Ethan` `Tyler` `Jason` `Chloe` `Veronica` `Victoria` `Miranda` `Sebastian` `Victor` `Malcolm` `Kayla` `Nate` `Jake` `Brian` `Amina` `Kelsey` `Derek` `Grant` `Evan` `Alex` `Ashley` `Craig` `Deborah` `Dennis` `Edward` `Elizabeth` `Hades` `Julia` `Pixie` `Mark` `Olivia` `Priya` `Ronald` `Sarah` `Shaun` `Theodore` `Timothy` `Wendy` `Dominus` `Hana` `Clive` `Carter` `Blake` `Luna`

#### [speed](https://runware.ai/docs/models/inworld-tts-1-5-max#request-speech-speed)

- **Path**: `speech.speed`
- **Type**: `float`
- **Min**: `0.5`
- **Max**: `1.5`
- **Step**: `0.1`
- **Default**: `1`

Playback speed of the generated speech.

**Settings**

Technical parameters to fine-tune the inference process. These must be nested inside the \`settings\` object.

### [temperature](https://runware.ai/docs/models/inworld-tts-1-5-max#request-settings-temperature)

- **Path**: `settings.temperature`
- **Type**: `float`
- **Min**: `0.1`
- **Max**: `2`
- **Step**: `0.01`
- **Default**: `1.1`

Controls randomness in generation. Lower values produce more deterministic outputs, higher values increase variation and creativity.

## Response Parameters

### [taskType](https://runware.ai/docs/models/inworld-tts-1-5-max#response-tasktype)

- **Type**: `string`
- **Required**: true
- **Value**: `audioInference`

Type of the task.

### [taskUUID](https://runware.ai/docs/models/inworld-tts-1-5-max#response-taskuuid)

- **Type**: `string`
- **Required**: true
- **Format**: `UUID v4`

UUID of the task.

### [audioUUID](https://runware.ai/docs/models/inworld-tts-1-5-max#response-audiouuid)

- **Type**: `string`
- **Required**: true
- **Format**: `UUID v4`

UUID of the output audio.

### [audioURL](https://runware.ai/docs/models/inworld-tts-1-5-max#response-audiourl)

- **Type**: `string`
- **Format**: `URI`

URL of the output audio.

### [audioBase64Data](https://runware.ai/docs/models/inworld-tts-1-5-max#response-audiobase64data)

- **Type**: `string`

Base64-encoded audio data.

### [audioDataURI](https://runware.ai/docs/models/inworld-tts-1-5-max#response-audiodatauri)

- **Type**: `string`
- **Format**: `URI`

Data URI of the output audio.

### [seed](https://runware.ai/docs/models/inworld-tts-1-5-max#response-seed)

- **Type**: `integer`

The seed used for generation. If none was provided, shows the randomly generated seed.

### [cost](https://runware.ai/docs/models/inworld-tts-1-5-max#response-cost)

- **Type**: `float`

Task cost in USD. Present when `includeCost` is set to `true` in the request.

## Examples

### Immersive Story Narration (Text to Audio)

[Listen to audio](https://assets.runware.ai/examples/inworld-tts-1-5-max/9b943f81-a2ee-4e29-8734-03b0215b86b3.mp3)

**Request**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "0fa1ab9f-3ed8-4b8b-aa9c-540b9eb6f07a",
  "model": "inworld:tts@1.5-max",
  "audioSettings": {
    "bitrate": 192,
    "sampleRate": 48000,
    "channels": 2
  },
  "speech": {
    "text": "When the storm finally loosened its grip on the valley, Mira stepped out onto the rain-slick stones and listened. No thunder. No shouting wind. Only the soft dripping of water from the pine branches and, somewhere in the silver fog below, the lonely bell of the harbor lighthouse calling through the dawn. She drew a careful breath, tasted salt and cedar in the air, and unfolded the letter she had carried across three countries. The ink had run at the edges, but the final line was still clear: When the sea grows quiet, come find me.",
    "voice": "Serena",
    "speed": 0.9
  },
  "settings": {
    "temperature": 1.05
  }
}
```

**Response**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "0fa1ab9f-3ed8-4b8b-aa9c-540b9eb6f07a",
  "audioUUID": "ceaf10cd-bb8b-40a5-94b3-cf2f87ae9a47",
  "audioURL": "https://am.runware.ai/audio/os/a03d21/ws/5/ai/ceaf10cd-bb8b-40a5-94b3-cf2f87ae9a47.mp3",
  "cost": 0.00536
}
```

---

### Mythic Trailer Narration (Text to Audio)

[Listen to audio](https://assets.runware.ai/examples/inworld-tts-1-5-max/83848a31-3422-4fa1-83dd-4203974f6340.mp3)

**Request**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "f3d5f422-48f8-407b-bcd1-5ca792df673d",
  "model": "inworld:tts@1.5-max",
  "audioSettings": {
    "bitrate": 192,
    "sampleRate": 48000,
    "channels": 2
  },
  "speech": {
    "text": "When the last ember faded, the kingdom did not fall in silence. It answered with steel, with thunder, and with the beating hearts of those who refused to kneel. Beyond the black cliffs, beneath a sky split by lightning, one rider carried the map, the oath, and the final spark of hope. By dawn, legends would awaken. By nightfall, the world would remember their names.",
    "voice": "Sebastian",
    "speed": 0.9
  },
  "settings": {
    "temperature": 1.12
  }
}
```

**Response**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "f3d5f422-48f8-407b-bcd1-5ca792df673d",
  "audioUUID": "17ac2403-f7b9-46db-9263-1ebcbdf3c21b",
  "audioURL": "https://am.runware.ai/audio/os/a17d13/ws/5/ai/17ac2403-f7b9-46db-9263-1ebcbdf3c21b.mp3",
  "cost": 0.00368
}
```

---

### Cinematic Story Narration (Text to Audio)

[Listen to audio](https://assets.runware.ai/examples/inworld-tts-1-5-max/32ae2e7a-b30d-4ea7-9adf-cdf3c9a12ed4.mp3)

**Request**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "1cf6413f-da48-42ba-9ded-515c239a8128",
  "model": "inworld:tts@1.5-max",
  "audioSettings": {
    "bitrate": 192,
    "sampleRate": 48000,
    "channels": 2
  },
  "speech": {
    "text": "When the last train vanished into the fog, Mara stepped onto the silent platform and unfolded the letter one final time. The ink had faded, but the promise still burned between the lines: at midnight, under the station clock, the truth would finally arrive. Around her, the city held its breath. Then, from somewhere deep in the mist, came the slow echo of approaching footsteps.",
    "voice": "Celeste",
    "speed": 0.9
  },
  "settings": {
    "temperature": 1.08
  }
}
```

**Response**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "1cf6413f-da48-42ba-9ded-515c239a8128",
  "audioUUID": "9a53c74c-51f6-4650-a3f0-619ed580074a",
  "audioURL": "https://am.runware.ai/audio/os/a07d11/ws/5/ai/9a53c74c-51f6-4650-a3f0-619ed580074a.mp3",
  "cost": 0.00379
}
```

---

### Emotive Story Narration (Text to Audio)

[Listen to audio](https://assets.runware.ai/examples/inworld-tts-1-5-max/625af8f2-fce4-4bcc-b715-d052ed15a22c.mp3)

**Request**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "3ccb5b6a-760e-41d8-a780-c0557bb1c2d5",
  "model": "inworld:tts@1.5-max",
  "audioSettings": {
    "bitrate": 192,
    "sampleRate": 48000,
    "channels": 2
  },
  "speech": {
    "text": "When the last train disappeared into the rain, Elena remained alone on the platform, clutching a letter softened by the storm. She had waited ten years for this moment, rehearsing a hundred different greetings, but now that the city lights trembled in the puddles and the night smelled of iron and sea salt, all her words felt small. Then she heard footsteps behind her—slow, familiar, impossible—and the world seemed to hold its breath.",
    "voice": "Serena",
    "speed": 0.9
  },
  "settings": {
    "temperature": 1.12
  }
}
```

**Response**:

```json
{
  "taskType": "audioInference",
  "taskUUID": "3ccb5b6a-760e-41d8-a780-c0557bb1c2d5",
  "audioUUID": "b858445e-416e-48c0-875f-362e45287354",
  "audioURL": "https://am.runware.ai/audio/os/a04d20/ws/5/ai/b858445e-416e-48c0-875f-362e45287354.mp3",
  "cost": 0.00437
}
```