MODEL ID inworld:tts@1.5-max

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Inworld TTS-1.5 Max

by Inworld AI January 21, 2026

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.

API Options

Platform-level options for task execution and delivery.

taskType string required value: audioInference: Identifier for the type of task being performed

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

outputType string default: URL: Audio output type.

Allowed values 3 values

outputFormat 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 4 values

webhookURL string 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
PLATFORM

deliveryMethod string default: sync

Determines how the API delivers task results.

Allowed values 2 values

: Returns complete results directly in the API response.
: Returns an immediate acknowledgment with the task UUID. Poll for results using getResponse.

Learn more 1 resource

Task Polling
PLATFORM

uploadEndpoint string 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.

// 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 integer min: 60: Time-to-live (TTL) in seconds for generated content. Only applies when outputType is URL.

includeCost boolean default: false: Include task cost in the response.

numberResults 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 object

Advanced settings for audio generation.

Properties 3 properties

audioSettings » bitrate bitrate integer min: 1: Target audio bitrate in kbps. Constraints depend on the output format.

audioSettings » sampleRate sampleRate integer min: 1000: Audio sample rate in Hz.

audioSettings » channels channels integer default: 2: Number of audio channels in the generated output (1 for Mono, 2 for Stereo).

Allowed values 2 values

model string required value: inworld:tts@1.5-max

Identifier of the model to use for generation.

Learn more 3 resources

speech object required

Settings for speech generation.

Properties 3 properties

speech » text text string required min: 2 max: 2000: Text to convert to speech.

speech » voice voice string required default: auto: Voice identifier to use. Set to auto for automatic selection.

Allowed values 73 values

speech » speed speed 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.

settings » temperature temperature 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.

taskType string required value: audioInference: Type of the task.

taskUUID string required UUID v4: UUID of the task.

audioUUID string required UUID v4: UUID of the output audio.

audioURL string URI: URL of the output audio.

audioBase64Data string: Base64-encoded audio data.

audioDataURI string URI: Data URI of the output audio.

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

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

Text to Audio

Immersive Story Narration

0:00

Request

{
  "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

{
  "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
}

Text to Audio

Mythic Trailer Narration

0:00

Request

{
  "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

{
  "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
}

Text to Audio

Cinematic Story Narration

0:00

Request

{
  "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

{
  "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
}

Text to Audio

Emotive Story Narration

0:00

Request

{
  "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

{
  "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
}