OpenAI TTS-1

Name: OpenAI TTS-1
Brand: OpenAI
SKU: openai-tts-1
Price: 0.018 USD
Availability: InStock

Text-to-speechAvailable

by OpenAIopenai-tts-1

OpenAI's text-to-speech model. Six built-in voices with natural intonation.

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Price: $0.018/1k chars
Input → output: Text → Audio
Developer: OpenAI
Updated: September 23, 2026

Playground

Try OpenAI TTS-1

Input & output

$0.018/1k chars

Text

Voice(optional)

Advanced settings (1)

Format(optional)

⌘/Ctrl + Enter

Output

The generated speech appears here.

This run

$0.0001 · 0.01 credits

New here?

10 free credits ($0.10) when you sign up with Google

Usable 24 hours after sign-up, up to 5 runs per day and at most 2 credits per run. Other sign-in methods start without credits. Enough for 1,000 runs of this model.

About OpenAI TTS-1

TL;DRAs of September 23, 2026

OpenAI TTS-1 is a model by OpenAI in the Text-to-speech category. On Railwail, OpenAI TTS-1 costs $0.018 per 1,000 characters.

Background

About OpenAI

Founded 2015 · San Francisco, California, USA

OpenAI was founded in December 2015 by Sam Altman, Elon Musk, Greg Brockman, Ilya Sutskever, Wojciech Zaremba and John Schulman as a non-profit AI research lab. It restructured into the capped-profit OpenAI LP in 2019 and has since received over $13B from Microsoft plus billions more from Thrive Capital, Sequoia, Khosla and SoftBank, at a 2024 valuation north of $157B and a planned 2025 round reportedly at $500B. The audio research line at OpenAI includes Jukebox (2020), Whisper (2022) and the TTS-1 family released in November 2023 alongside the ChatGPT voice feature. TTS-1 powers ChatGPT Voice Mode, the OpenAI API audio endpoint and the Realtime API used in voice agents.

Visit OpenAI

Architecture

Proprietary Transformer text-to-speech with neural codec

OpenAI TTS-1 is the standard-quality variant of OpenAI's text-to-speech model family, optimised for real-time streaming inside ChatGPT Voice and the Realtime API. It is a Transformer-based model that predicts neural-codec audio tokens conditioned on text and a fixed set of stock voices (alloy, echo, fable, onyx, nova, shimmer) that OpenAI recorded with professional voice talent. There is no voice cloning. The model supports six output formats (MP3, Opus, AAC, FLAC, WAV, PCM) and outputs at 24 kHz. TTS-1 is tuned for low latency and starts streaming audio within a few hundred milliseconds, making it suitable for live conversational agents, while the HD sibling trades latency for fidelity. Text input is capped at 4,096 characters per request. OpenAI has not published a technical paper but the system architecturally resembles published neural-codec TTS such as VALL-E.

Parameters: Undisclosed
Context: 4,096 tokens

Capabilities

Real-time streaming TTS with sub-second first-byte latency
Six recorded voices: alloy, echo, fable, onyx, nova, shimmer
Multilingual: 50+ languages including English, German, Spanish, French, Italian, Japanese, Mandarin
Six output formats including streaming PCM for low latency
Powers ChatGPT Voice and the OpenAI Realtime API
Inexpensive at $0.015 per 1,000 characters (vs. $0.03 for HD)
Best for: voice agents, IVR, interactive narration, accessibility

Training & license

Not disclosed. OpenAI states voices were recorded with paid professional voice actors and the model was trained on a mixture of recorded speech and licensed text-audio pairs.

License: Proprietary commercial API. Generated audio may be used commercially under the OpenAI Usage Policy; the six stock voices cannot be impersonated outside the API.

Safety testing: OpenAI's Preparedness team red-teamed Voice Mode; outputs include watermark provenance metadata in the Realtime API where supported. Voice cloning is intentionally not exposed.

Known limitations

No custom voice cloning
Limited prosody / emotion control
Quality below TTS-1 HD on slow, emotional narration
Hard cap of 4,096 characters per request
Closed weights, hosted only

Research papers

Pricing

Prices in US dollars. Usage is charged from prepaid credits.

1,000 characters	$0.018 per 1,000 characters

1 credit = $0.01

Cost calculator

Price calculator

Characters per run

/ run

Runs

Total

$1.80

180 credits

Per run

$0.018 · 1.8 credits

Fixed price per run, known before the run starts.

API

Call OpenAI TTS-1 with your Railwail API key. Use this model ID in the request:

openai-tts-1API documentation Get an API key

curl https://railwail.com/api/v1/audio/speech \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai-tts-1",
    "input": "Hello from railwail. This sentence was spoken by a text-to-speech model.",
    "voice": "alloy"
  }' \
  --output speech.mp3

import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["RAILWAIL_API_KEY"],
    base_url="https://railwail.com/api/v1",
)

with client.audio.speech.with_streaming_response.create(
    model="openai-tts-1",
    input="Hello from railwail. This sentence was spoken by a text-to-speech model.",
    voice="alloy",
) as response:
    response.stream_to_file("speech.mp3")

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

const client = new OpenAI({
  apiKey: process.env.RAILWAIL_API_KEY,
  baseURL: "https://railwail.com/api/v1",
});

const speech = await client.audio.speech.create({
  model: "openai-tts-1",
  input: "Hello from railwail. This sentence was spoken by a text-to-speech model.",
  voice: "alloy"
});

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

Set your key as RAILWAIL_API_KEYCreate API key

Specifications

Model ID: openai-tts-1
Developer: OpenAI
Category: Text-to-speech
Input: Text
Output: Audio
Output formats: MP3, OPUS, AAC, FLAC
Billing: Fixed price, known before the run
Model size: Undisclosed
License: Proprietary commercial API. Generated audio may be used commercially under the OpenAI Usage Policy; the six stock voices cannot be impersonated outside the API.
Catalog entry updated: September 23, 2026

Input parameters

Inputs and settings from the model's input schema. The example in the API section shows which of them the API accepts.

ParameterTypeDefaultAllowed values

textrequired
Type: Text
Default: –
Allowed values: –
voice
Type: Choice
Default: –
Allowed values: alloy, echo, fable, onyx, nova, or shimmer
response_format
Type: Choice
Default: –
Allowed values: mp3, opus, aac, or flac

Example prompts

Examples from the Railwail catalog. They were not generated live on this page.

Notification Voice
Your order has been confirmed and is being prepared. Estimated delivery time is thirty-five minutes. You'll receive a notification when your driver is on the way.
Tutorial Guide
Step one: open your terminal and navigate to the project directory. Step two: run npm install to download all dependencies. Step three: create a dot env file and add your API keys. Finally, run npm run dev to start the development server.

Use cases

What it is used for

Real-time voice agents
ChatGPT Voice and conversational tutors
IVR and phone bot replies
Accessibility narration for web and mobile
Notification and alert audio

Related guides

AI Voice & Text-to-Speech Models

All models in Text-to-speech

Frequently asked questions

What is OpenAI TTS-1?

OpenAI TTS-1 is a model by OpenAI in the Text-to-speech category. On Railwail you can call it with an API key through the Railwail API.

How much does OpenAI TTS-1 cost on Railwail?

On Railwail, OpenAI TTS-1 costs $0.018 per 1,000 characters. The price is known before the run starts. Usage is paid from prepaid credits; 1 credit equals $0.01.

Which settings does OpenAI TTS-1 support?

According to its input schema, OpenAI TTS-1 knows these parameters: text, voice (alloy, echo, fable, onyx, nova, or shimmer), and response_format (mp3, opus, aac, or flac).

How fast is OpenAI TTS-1?

There are not enough measured runs of OpenAI TTS-1 on Railwail yet to state a run time. It depends on the input, the settings and the load at the provider.

Is OpenAI TTS-1 better than AudioLDM 2?

That depends on the task. OpenAI TTS-1 (OpenAI) and AudioLDM 2 (Haohe Liu) are both models in the Text-to-speech category. The comparison page shows their prices and specifications side by side.

Compare OpenAI TTS-1 and AudioLDM 2

How do I use OpenAI TTS-1 through the API?

Create a Railwail API key and send your request with the model ID openai-tts-1. Code examples for curl, Python and JavaScript are in the API section of this page.

Comparable models

All in this category

ChatterboxResemble AI
Resemble AI's open Chatterbox TTS. Zero-shot voice cloning from a short audio prompt with an exaggeration control for emotion intensity, plus CFG weight to balance pacing and fidelity.
$0.030/1k chars
67 % more expensive per unit
Compare OpenAI TTS-1 vs. Chatterbox
OpenAI TTS-1 HDOpenAI
OpenAI's high-definition TTS model. Better quality for production use cases.
$0.036/1k chars
100 % more expensive per unit
Compare OpenAI TTS-1 vs. OpenAI TTS-1 HD
Qwen3 TTSAlibaba (Qwen)
A unified Text-to-Speech demo featuring three powerful modes: Voice, Clone and Design
$0.024/1k chars
33 % more expensive per unit
Compare OpenAI TTS-1 vs. Qwen3 TTS

Use OpenAI TTS-1 via the API

One API key for every model on Railwail. Usage is charged from prepaid credits, 1 credit = $0.01.

Get API key Browse all models