Fish Audio open-sources S2
Expressive 80+ language TTS with inline emotion tags
Confirmed
Status
- Claim
Confirmed
- Our reporting
- High confidence
- Importance
- 3 of 5
- Last verified
- 13 October 2026
Your AI and this story
- GPT-6 AstraIn its training data
- Claude Opus 5.5In its training data
- Gemini 4 HydrogenIn its training data
- Grok 4.7In its training data
It happened before the cutoffs of all four assistants, so it can be in their training data.
Key facts
- Dual-AR: 4B time-axis + 400M depth-axis; RTF 0.195, ~100 ms TTFA
- Seed-TTS Eval WER 0.54% (zh) / 0.99% (en); EmergentTTS-Eval win rate 81.88%
- API id s2-pro, $15 per 1M UTF-8 bytes; weights under Fish Audio Research License (non-commercial)
- S2.1 Pro (2026-06-23): free API tier
s2.1-pro-freethrough 2026-11-30, ~90 ms TTFA, 83 languages; weights not released
What happened
Fish Audio shipped S2 as a complete system: weights, fine-tuning code and a serving stack compatible with LLM-inference optimizations (SGLang). Emotion is controlled inline with natural-language tags.
Why it matters
It made open TTS with fine-grained, LLM-style prompt control and production streaming available to the public, and set the open-weights bar for most of 2026. Fish Audio’s later move to a free closed API (S2.1 Pro) shows price pressure in hosted TTS.
Sources
4 sources from 3 sites. Numbers match the chips in the text.
4 sources: 4 primary
Primary
- Fish Audio: open-sourcing S2fish.audio, official
- Fish Audio S2 Technical Report (arXiv 2603.08823)arxiv.org, paper
- Hugging Face: fishaudio/s2-prohuggingface.co, code
- Fish Audio: S2.1 Pro free APIfish.audio, official
Changes
- Linked the successor Drama 3 (released 2026-10-13 under a revenue-capped Community License; S2 Pro weights stay under the Research License) and the July 2026 seed round
- Filed