GPT-4o mini TTS: Complete Specifications, Pricing, API Access & Use Cases (2026)

What is GPT-4o mini TTS?

GPT-4o mini TTS is OpenAI’s controllable text-to-speech model, released on March 20, 2025, with a maximum input length of 2,000 tokens and token-based API pricing of $ 0.60 per million text-input tokens and $ 12 per million audio-output tokens as of July 2026.

The model converts written text into generated speech rather than returning a conventional text response. It is built on the GPT-4o mini architecture and is designed for applications that need natural-sounding narration, streamed speech, multilingual audio, or control over how a line is spoken.

Unlike the general GPT-4o mini model family , GPT-4o mini TTS has a specialized modality profile: text is input and audio is output. It is not a general chat model, transcription model, image model, or speech-to-speech reasoning model.

What Are GPT-4o mini TTS’s Key Specifications and Pricing?

OpenAI’s model documentation confirms the 2,000-token maximum input, text-only input modality, audio-only output modality, and published token rates. The documented speech-generation endpoint is /v1/audio/speech .

As per the Gate.AI model-card, the catalog entry is identified as openai/gpt-4o-mini-tts . For the dedicated Gate.AI text-to-speech endpoint, the request body uses gpt-4o-mini-tts as the model value. This distinction matters because catalog identifiers and endpoint request values ​​are not always interchangeable. Gate.AI documents an OpenAI-compatible base URL of documented https://api.gate.ai/openai/v1 .

What Can GPT-4o mini TTS Do That Makes It Useful in Production?

Control how speech is delivered

Developers can use natural-language instructions to influence accent, emotional range, intonation, speaking speed, tone, impressions, and whispering. This makes the model relevant for customer-service prompts, educational narration, character dialogue, and branded audio experiences. Output should still be reviewed when exact pronunciation or emotional delivery is important.

Stream audio before the full response is complete

OpenAI supports streamed speech generation, allowing playback to begin before the complete audio file is available. Gate.AI also documents server-sent event streaming through stream_format: "sse" , where audio is returned in encoded chunks followed by usage and billing metadata.

Generate several standard audio formats

OpenAI documents MP3, Opus, AAC, FLAC, WAV, and PCM output. MP3 is suitable for general distribution, Opus for internet communication, FLAC for lossless storage, and WAV or PCM for workflows where low decoding overhead matters.

Produce speech in multiple languages

The text-to-speech guide lists support across many languages, including English, Chinese, Japanese, Korean, French, German, Spanish, Arabic, Hindi, Portuguese, and Vietnamese. OpenAI notes that its built-in voices are optimized for English, so multilingual pronunciation and naturalness should be tested with representative scripts.

Select from built-in voices

OpenAI documents 13 built-in voices: alloy , ash , ballad , coral , echo , fable , nova , onyx , sage , shimmer , verse , marin , and cedar . Voice availability can vary by model, and OpenAI recommends marin or cedar for quality-focused use cases.

What Are GPT-4o mini TTS’s Supported Modalities?

GPT-4o mini TTS should not be confused with the broader GPT-4o multimodal model . GPT-4o mini TTS is purpose-built for text-to-audio generation and does not expose the wider input and reasoning capabilities associated with general multimodal models.

Where Does GPT-4o mini TTS Fall Short?

The 2,000-token input limit makes the model less convenient for long-form documents, audiobooks, or extended training material. Longer scripts must be divided into segments, and teams may need to manage pacing, pronunciation, pauses, and voice consistency across those segments.

Although multilingual speech is supported, the built-in voices are optimized for English. Quality can vary by language, accent, proper noun, acronym, or technical term, so representative testing is necessary before release.

The standard text-to-speech guide does not document fine-grained phoneme controls for every pronunciation case. Teams may need to adjust spelling, punctuation, wording, or segmentation to improve difficult names and specialist terminology.

Custom voices are limited to eligible OpenAI customers. Their creation requires a consent recording and a separate sample recording, so standard API access should not be treated as automatic access to voice cloning or organization-specific voices.

Generated speech can contain pronunciation mistakes, unintended emphasis, or unsuitable emotional delivery. This is a general generative-AI limitation rather than a model-specific safety guarantee. Medical, legal, financial, emergency, and other high-impact audio should be reviewed by a qualified person before publication or use.

OpenAI also requires applications to disclose clearly that the listener is hearing an AI-generated voice rather than a human speaker.

What Is GPT-4o mini TTS Best Used For?

How Does GPT-4o mini TTS Compare to TTS-1 and TTS-1-HD?

OpenAI describes GPT-4o mini TTS as its newest and most reliable text-to-speech model. It positions TTS-1 as the lower-latency model and TTS-1-HD as the higher-quality option within the older model pair. No model is universally preferable; the practical choice depends on voice quality, instruction control, language performance, latency, and integration requirements.

How Do I Access GPT-4o mini TTS Through Gate.AI?

Gate.AI documents an OpenAI-compatible text-to-speech API with the base URL https://api.gate.ai/openai/v1 and the endpoint POST /audio/speech . Requests use a Gate.AI API key in the bearer authorization header and send a JSON body containing the model, input text, and voice.

As per the Gate.AI model-card, the model’s catalog identifier is openai/gpt-4o-mini-tts . In the dedicated TTS request schema, Gate.AI documents gpt-4o-mini-tts as the accepted model value.

By default, Gate.AI returns binary audio synchronously. Setting stream_format to sse returns speech.audio.delta events containing encoded audio chunks and a final speech.audio.done event containing usage and billing details.

Python Example

Python import os

from pathlib import Path

import requests

api_key = os.environ["GATEAI_API_KEY"]
output_file = Path("speech.mp3")

response = requests.post(
"https://api.gate.ai/openai/v1/audio/speech",
headers={
"Authorization": f"Bearer {api_key}",
"Content-Type": "application/json",
},
json={
"model": "gpt-4o-mini-tts",
"input": "Welcome to this GPT-4o mini TTS demonstration.",
"voice": "alloy",
"response_format": "mp3",
},
timeout=120,
)

response.raise_for_status()
output_file.write_bytes(response.content)

print(f"Audio saved to {output_file}") ```

curl Example

``` Bash curl https://api.gate.ai/openai/v1/audio/speech \

-H "Authorization: Bearer $GATEAI_API_KEY" \
-H "Content-Type: application/json" \
-d ‘{
"model": "gpt-4o-mini-tts",
"input": "Welcome to this GPT-4o mini TTS demonstration.",
"voice": "alloy",
"response_format": "mp3
}’ \
—output speech.mp3

The code follows Gate.AI’s documented base URL, bearer authentication method, endpoint path, request fields, model value, and binary response behavior.

FAQs

What is the maximum input length for GPT-4o mini TTS?

GPT-4o mini TTS accepts up to 2,000 input tokens per request as of July 2026. Longer scripts must be divided into smaller sections before speech generation.

How much does GPT-4o mini TTS cost?

OpenAI lists GPT-4o mini TTS at \ $ 0.60 per million text-input tokens and \ $ 12 per million audio-output tokens as of July 2026. Total cost depends on the text submitted and the audio tokens generated.

How can developers access GPT-4o mini TTS through Gate.AI?

Developers can send an authenticated request to Gate.AI’s /openai/v1/audio/speech endpoint. The JSON body includes gpt-4o-mini-tts , the input text, a voice, and an optional response format.

When may GPT-4o mini TTS be preferable to TTS-1 or TTS-1-HD?

GPT-4o mini TTS may fit applications that need natural-language control over tone, accent, pace, emotional delivery, or intonation. TTS-1 remains positioned for lower latency, while TTS-1-HD is the higher-quality model in OpenAI’s older TTS pair.