Text-to-speech technology has undergone a revolution. Just two years ago, the best open source TTS models sounded robotic and unnatural. Today, models like Kokoro and Chatterbox produce speech that's nearly indistinguishable from human recordings — and they're completely free to use.
Why Open Source TTS Matters
Commercial TTS APIs charge per character and lock you into proprietary ecosystems. Open source models give you full control: run them on your own hardware, customize voices, and scale without per-request costs. With permissive licenses like Apache 2.0 and MIT, you can use them in commercial products without restrictions.
Top Open Source TTS Models
Kokoro — Best Overall (Apache 2.0)
Kokoro is an 82 million parameter model that punches far above its weight. Despite being tiny compared to competitors, it generates studio-quality speech nearly 100x faster than real-time on a GPU. It supports English, Japanese, Chinese, Korean, French, German, Italian, Portuguese, Spanish, Hindi, and Russian with expressive voices. If you need one model that does everything well, start here.
Chatterbox — Best for Voice Cloning (MIT)
Developed by Resemble AI, Chatterbox excels at voice cloning from short reference audio. Upload a few seconds of speech, and it produces remarkably accurate reproductions. It includes a built-in audio watermark for responsible use. MIT licensed with no commercial restrictions.
CosyVoice2 — Best Multilingual (Apache 2.0)
Alibaba's CosyVoice2 handles multilingual speech synthesis with exceptional quality. It supports voice cloning and produces natural-sounding output across dozens of languages. Apache 2.0 licensed, making it suitable for any commercial application.
Dia — Best for Dialogue (Apache 2.0)
Nari Labs' Dia specializes in conversational speech with multiple speakers. It generates realistic dialogue including non-verbal cues like laughter and pauses. At 1.6 billion parameters, it's larger than Kokoro but produces uniquely expressive conversational audio.
Sesame CSM — Most Expressive (Apache 2.0)
Sesame's Conversational Speech Model focuses on emotional expressiveness. It captures subtle vocal nuances that other models miss — hesitation, emphasis, warmth. Ideal for audiobooks, podcasts, and any content where emotional delivery matters.
Orpheus — Best Emotional Range (Llama 3.2)
Built on Meta's Llama 3.2 architecture, Orpheus uses SNAC audio tokens for high-fidelity output. It handles emotion tags naturally, letting you control the emotional tone of generated speech. Requires "Built with Llama" attribution.
Quick Comparison
| Model | License | Speed | Quality | Voice Cloning |
|---|---|---|---|---|
| Kokoro | Apache 2.0 | Ultra-fast | Excellent | No |
| Chatterbox | MIT | Medium | Excellent | Yes |
| CosyVoice2 | Apache 2.0 | Medium | Excellent | Yes |
| Dia | Apache 2.0 | Slow | Excellent | No |
| Sesame CSM | Apache 2.0 | Medium | Excellent | No |
| Orpheus | Llama 3.2 | Medium | Very Good | No |
Getting Started
You can try all of these models for free at TTS.ai — no account required for free-tier models like Kokoro. For API access, install our Python or JavaScript SDK:
pip install ttsainpm install @ttsainpm/ttsaiWhat's Coming Next
The TTS landscape evolves rapidly. We're tracking upcoming models like Chatterbox Turbo, Zonos, and Dia2 — all Apache 2.0 licensed. As new models launch, we add them to TTS.ai so you can compare quality and speed across every option in one place.