Inworld TTS 2 Text to Speech and Voice Cloning API

Inworld TTS 2

curl --request POST \
  --url https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice

const options = {method: 'POST'};

fetch('https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice"

	req, _ := http.NewRequest("POST", url, nil)

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

require 'uri'
require 'net/http'

url = URI("https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)

response = http.request(request)
puts response.read_body

POST

inworld-tts-2

tts

voice

Inworld TTS 2

curl --request POST \
  --url https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice

const options = {method: 'POST'};

fetch('https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice"

	req, _ := http.NewRequest("POST", url, nil)

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

require 'uri'
require 'net/http'

url = URI("https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)

response = http.request(request)
puts response.read_body

1. Overview

This document describes how to use speech synthesis and voice cloning through the Inworld TTS native protocol. Both endpoints are synchronous: a POST request returns the result directly, with no need to create a task and poll for the result.

1.1 Endpoints

Capability	Method and path
Speech synthesis	`POST /v3/inworld-tts-2/tts/v1/voice`
Voice cloning	`POST /v3/inworld-tts-2/voices/v1/voices:clone`

The full address in the examples in this document is https://api.novita.ai plus the endpoint path in the table above, where https://api.novita.ai is the API domain you use.

1.2 Authentication

All requests must carry the platform API Key and specify the JSON content type:

Authorization: Bearer <YOUR_API_KEY>
Content-Type: application/json

1.3 Response Structure

Both endpoints return JSON on success:

In the JSON returned by a successful speech synthesis request, audioContent is Base64-encoded audio data that must be decoded to obtain the raw audio bytes.
In the JSON returned by a successful voice cloning request, voice.voiceId is the ID of the newly cloned voice, which can be used directly as the voiceId field of the speech synthesis endpoint.

2. Speech Synthesis

Official parameter reference: Synthesize Speech

2.1 Endpoint

POST https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice

Common request fields:

Field	Type	Required	Description
`text`	string	Yes	Text to synthesize, up to 2000 UTF-16 code units.
`voiceId`	string	Yes (either this or `voiceDesign`)	Voice ID to use. You can use a built-in voice (such as `Ashley`) or a `voiceId` produced by the voice cloning endpoint.
`modelId`	string	Yes	Model to use, fixed to `inworld-tts-2`.
`language`	string	No	BCP-47 language tag (such as `en-US`). If omitted, the language is detected automatically.
`deliveryMode`	string	No	Defaults to `DELIVERY_MODE_UNSPECIFIED`. Options are `STABLE`/`BALANCED`/`CREATIVE`. Takes effect only on `inworld-tts-2` and controls how much the output varies.
`temperature`	number	No	Defaults to 1, range `(0, 2]`. This field is ignored on the `inworld-tts-2` model.
`timestampType`	string	No	Defaults to `TIMESTAMP_TYPE_UNSPECIFIED`. Options are `WORD`/`CHARACTER`, returning timestamp metadata at the corresponding granularity.
`applyTextNormalization`	string	No	Defaults to `APPLY_TEXT_NORMALIZATION_UNSPECIFIED`. Options are `ON`/`OFF`, controlling whether numbers, dates, and abbreviations are expanded before synthesis.
`enhanceGeneration`	boolean	No	Defaults to `false`. When enabled, noise reduction is applied to the output.
`audioConfig.audioEncoding`	string	No	Defaults to `MP3`. Options are `LINEAR16`/`MP3`/`OGG_OPUS`/`ALAW`/`MULAW`/`FLAC`/`PCM`/`WAV`.
`audioConfig.bitRate`	integer	No	Takes effect only for compressed formats. Defaults to 128000 (in bit/s).
`audioConfig.sampleRateHertz`	integer	No	Range 8000–48000.
`audioConfig.speakingRate`	number	No	Defaults to 1.0, range 0.5–1.5. Controls the speaking rate.

voiceId and voiceDesign (instant voice design, out of scope of this document) are mutually exclusive; do not provide both.

2.2 Example

curl -X POST 'https://api.novita.ai/v3/inworld-tts-2/tts/v1/voice' \
  -H 'Authorization: Bearer <YOUR_API_KEY>' \
  -H 'Content-Type: application/json' \
  -d '{
    "text": "Hello world",
    "voiceId": "Ashley",
    "modelId": "inworld-tts-2"
  }'

2.3 Response

On success, the endpoint returns (HTTP 200):

{
  "audioContent": "<base64-encoded-audio>"
}

Field	Type	Description
`audioContent`	string	Base64-encoded audio data, up to 16MB after decoding. The default encoding is `MP3` and can be changed with `audioConfig.audioEncoding`.
`usage.processedCharactersCount`	integer	Number of characters processed by this request (usage information).
`usage.modelId`	string	Model used for this synthesis.
`timestampInfo.wordAlignment`	object	Returned when the request sets `timestampType=WORD`, containing the start and end time of each word.
`timestampInfo.characterAlignment`	object	Returned when the request sets `timestampType=CHARACTER`, containing the start and end time of each character.

Verified in practice: this endpoint has been validated with real requests in all three platform environments and returns real audioContent.

2.4 Billing

Request cost = unit price (per million characters) × number of characters in text / 1000000

The character count is calculated from the text field. Chinese characters count as 2 characters, and other characters (including English letters, digits, spaces, and punctuation) count as 1 character. The exact unit price depends on the pricing page of the service you use.

3. Voice Cloning

Official parameter reference: Clone a Voice

3.1 Endpoint

POST https://api.novita.ai/v3/inworld-tts-2/voices/v1/voices:clone

The request body is JSON. Common fields:

Field	Type	Required	Description
`displayName`	string	Yes	Display name of the cloned voice.
`voiceSamples`	array	Yes	List of audio samples used for cloning.
`voiceSamples[].audioData`	string	Yes	Base64-encoded WAV or MP3 audio. 10–30 seconds is recommended; anything longer than 30 seconds is truncated.
`voiceSamples[].transcription`	string	No	Transcription of the sample. Generated automatically if omitted.
`langCode`	string	No	Language (legacy uppercase underscore format, such as `EN_US`). Mutually exclusive with `languageCode`; do not provide both. `AUTO` means automatic detection.
`languageCode`	string	No	Language (standard format, such as `en-US`). The language is detected automatically when omitted or set to `"auto"`.
`description`	string	No	Description of the voice’s tone, accent, or purpose, to make it easier to find.
`tags`	array	No	Free-form tags used for filtering and grouping. Gender and age cannot be set through this field; values passed in are silently ignored.
`audioProcessingConfig.removeBackgroundNoise`	boolean	No	Whether to separate background noise from the sample. If the original audio is already clean, enabling this may reduce quality instead.

gender/ageGroup/categories cannot be set during cloning. Call UpdateVoice separately after cloning is complete to set them.

3.2 Example

curl -X POST 'https://api.novita.ai/v3/inworld-tts-2/voices/v1/voices:clone' \
  -H 'Authorization: Bearer <YOUR_API_KEY>' \
  -H 'Content-Type: application/json' \
  -d '{
    "displayName": "my-cloned-voice",
    "voiceSamples": [
      {
        "audioData": "<base64-encoded-audio>"
      }
    ]
  }'

3.3 Response

On success, the endpoint returns (HTTP 200):

{
  "voice": {
    "voiceId": "<workspace_id>__my-cloned-voice",
    "displayName": "my-cloned-voice",
    "source": "IVC"
  },
  "audioSamplesValidated": [
    {
      "langCode": "EN_US",
      "transcription": "...",
      "warnings": [],
      "errors": []
    }
  ]
}

Field	Type	Description
`voice.voiceId`	string	ID of the cloned voice, used directly as the `voiceId` field of the speech synthesis endpoint. The format is `{workspace}__{voice name}`.
`voice.displayName`	string	Echoes the display name from the request.
`voice.source`	string	Fixed to `IVC` for instant cloning.
`audioSamplesValidated[].langCode`	string	Language of the sample, either detected or specified.
`audioSamplesValidated[].transcription`	string	Transcription of the sample.
`audioSamplesValidated[].warnings`/`.errors`	array	Lists of non-fatal/fatal issues encountered while processing the sample.

Verified in practice: the full “clone → synthesize with the cloned voiceId” path has been validated with real requests in all three platform environments.

3.4 Billing

The voice cloning endpoint is always free of charge and generates no cost.

4. Common Errors and Notes

Endpoint errors use the following structure:

{
  "code": "<error code>",
  "message": "<error message>"
}

HTTP	Common scenario	Suggested handling
400	Invalid request parameters, such as missing fields, wrong format, or `text` too long.	Fix the request based on the error message.
401	API Key missing or invalid.	Check the `Authorization` request header.
404	The `voiceId` used does not exist or is not accessible.	Check the value of the `voiceId` field.
429	Too many requests (voice cloning is rate limited more strictly than speech synthesis).	Reduce the request rate and use exponential backoff.
500	Temporary service error.	Retry later. If the failure persists, contact technical support.

Other notes:

A voiceId created by voice cloning is shared among all callers under the current API Key, and the system does not record which caller cloned which voice. Manage voice ownership and visibility in your own business layer, and do not assume the platform isolates voices between callers.
Supported audio formats for the voice cloning endpoint are wav/mp3/webm, with a maximum of 12MB per file.

Last modified on October 20, 2026

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Inworld TTS 2

1. Overview

1.1 Endpoints

1.2 Authentication

1.3 Response Structure

2. Speech Synthesis

2.1 Endpoint

2.2 Example

2.3 Response

2.4 Billing

3. Voice Cloning

3.1 Endpoint

3.2 Example

3.3 Response

3.4 Billing

4. Common Errors and Notes

​1. Overview

​1.1 Endpoints

​1.2 Authentication

​1.3 Response Structure

​2. Speech Synthesis

​2.1 Endpoint

​2.2 Example

​2.3 Response

​2.4 Billing

​3. Voice Cloning

​3.1 Endpoint

​3.2 Example

​3.3 Response

​3.4 Billing

​4. Common Errors and Notes

1. Overview

1.1 Endpoints

1.2 Authentication

1.3 Response Structure

2. Speech Synthesis

2.1 Endpoint

2.2 Example

2.3 Response

2.4 Billing

3. Voice Cloning

3.1 Endpoint

3.2 Example

3.3 Response

3.4 Billing

4. Common Errors and Notes