Gradium open-sources Phonon, on-device text-to-speech models under 50M parameters that run with no GPU; only the English 31m model is licensed for commercial use

Why it matters

【Key points】

Gradium open-sourced Phonon on Oct 20: on-device text-to-speech models under 50M parameters that run locally with no GPU or network.

1. Variants: Phonon 31m is English-only, about 64 MB, Apache 2.0 (commercial use allowed). Phonon 40m comes as five single-language models (EN, FR, DE, ES, PT), and Phonon 40m multilingual covers all five in one model. Both are CC BY-NC; commercial use needs a Gradium license.

2. Speed (Gradium's tests): first audio in about 7 ms on a MacBook Air M5 CPU versus 517 ms for Kokoro; 38 ms and 3.7x real time on a Raspberry Pi 5. Qualcomm measured 7.5 ms on the Snapdragon 8 Elite Gen 5; Arm measured 28 ms on Arm CPUs.

3. Accuracy (Gradium's tests): on 500 hard English sentences (phone numbers, emails, postal codes) the 31m model has a 1.70% word error rate versus 3.50% for Kokoro. The test set is public.

4. Day-0 support in Hugging Face Transformers, Ollama, LM Studio and MLX-Audio; runs in browsers, on iPhone and Apple Watch. 100+ built-in voices, plus voices cloned or designed on Gradium's platform.

5. It builds on Kyutai's Pocket TTS research.

【Verifiable】

Announcement: https://gradium.ai/blog/release-phonon-open-weight

Launch post: https://x.com/GradiumAI/status/2112563128487514512

Model: https://huggingface.co/gradium/phonon-31m-en

Multilingual: https://huggingface.co/gradium/phonon-40m-multilingual

Code: https://github.com/gradium-ai/xn-ptts

Test set: https://huggingface.co/datasets/gradium/tts-hard-sentences-202610

【Our read】

1. Local speech gets cheaper again: a model of a few dozen MB talks in real time on phones, watches and in browsers, useful for game characters, offline assistants and privacy-sensitive apps.

2. Only the English 31m model is free for commercial use; the multilingual and higher-quality 40m models are non-commercial.

3. Speed and accuracy figures come from Gradium and its partners, mostly against small models like Kokoro; no third-party leaderboard results yet.