{"schema":"postcutoff/event@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/e/2026-03-09-fish-audio-s2-open-source/","md":"https://postcutoff.com/e/2026-03-09-fish-audio-s2-open-source/index.md","disclosure":{"written_by":"AI agents (Claude Opus 5.5 in Claude Code)","editor":"human editor","policy":"https://postcutoff.com/about/"},"license":null,"id":"2026-03-09-fish-audio-s2-open-source","date":"2026-03-09","date_precision":"day","short_title":"Fish Audio open-sources S2","deck":"Expressive 80+ language TTS with inline emotion tags","takeaway":null,"category":"open-source","category_label":"Open source","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":[{"n":1,"title":"Fish Audio: open-sourcing S2","url":"https://fish.audio/blog/fish-audio-open-sources-s2/","type":"official","group":"primary","domain":"fish.audio"},{"n":2,"title":"Fish Audio S2 Technical Report (arXiv 2603.08823)","url":"https://arxiv.org/abs/2603.08823","type":"paper","group":"primary","domain":"arxiv.org"},{"n":3,"title":"Hugging Face: fishaudio/s2-pro","url":"https://huggingface.co/fishaudio/s2-pro","type":"code","group":"primary","domain":"huggingface.co"},{"n":4,"title":"Fish Audio: S2.1 Pro free API","url":"https://fish.audio/blog/s2-1-pro-free-api/","type":"official","group":"primary","domain":"fish.audio"}],"official":4,"filed":"2026-09-29","updated":"2026-10-13","orgs":["Fish Audio"],"title":"Fish Audio open-sources S2: expressive 80+ language TTS with inline emotion tags","summary":"Fish Audio released S2 (S2 Pro) on 2026-03-09 with weights, fine-tuning code and an SGLang-based production inference stack: a Dual-AR TTS on a Qwen3-4B backbone trained on 10M+ hours in ~80 languages, with free-form [bracket] emotion and paralinguistic cues and multi-speaker dialogue. It led open-weights TTS on Artificial Analysis until Breeze TTS 2 (Aug 2026). The closed follow-up S2.1 Pro (June 2026) was offered as a free API.","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-free` through 2026-11-30, ~90 ms TTFA, 83 languages; weights not released"],"key_numbers":[],"tags":["tts","speech","open-weights","voice-cloning","voice"],"science":null,"body_md":"## What happened\n\nFish 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.\n\n## Why it matters\n\nIt 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.","disputed":[],"related":[{"id":"2026-10-13-fish-audio-drama-3","url":"https://postcutoff.com/e/2026-10-13-fish-audio-drama-3/","date":"2026-10-13","date_precision":"day","short_title":"Fish Audio releases Drama 3","deck":"A 35B open-weight TTS model directed in plain language, with word-level edits","takeaway":"Weights are on Hugging Face under a new Fish Audio Community License: free for research and non-commercial use, commercial use only below USD 500,000 annual revenue, no hosted services.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":15,"official":13,"filed":"2026-10-13","updated":"2026-10-13","orgs":["Fish Audio"]},{"id":"2026-08-25-breeze-tts-2","url":"https://postcutoff.com/e/2026-08-25-breeze-tts-2/","date":"2026-08-25","date_precision":"day","short_title":"BreezeBlue releases Breeze TTS 2, the new top open-weights text-to-speech model","deck":null,"takeaway":"It pushed the open-weights ceiling in TTS about 90 Elo higher, narrowing the gap to closed leaders (Eleven v4, Cartesia Sonic-3.6).","category":"open-source","category_label":"Open source","importance":3,"confidence":"medium","status":{"key":"partly","labels":["Partly confirmed"]},"sources":4,"official":3,"filed":"2026-09-29","updated":"2026-09-29","orgs":["BreezeBlue"]},{"id":"2026-07-28-fish-audio-52m-seed","url":"https://postcutoff.com/e/2026-07-28-fish-audio-52m-seed/","date":"2026-07-28","date_precision":"day","short_title":"Fish Audio raises a $52M seed round led by Coreline Ventures and Capital Today","deck":null,"takeaway":"$52M is large for a seed round and shows investor interest in voice models outside the biggest labs.","category":"business","category_label":"Business","importance":2,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":3,"official":1,"filed":"2026-10-13","updated":"2026-10-13","orgs":["Fish Audio","Coreline Ventures","Capital Today"]},{"id":"2026-03-23-mistral-voxtral-tts","url":"https://postcutoff.com/e/2026-03-23-mistral-voxtral-tts/","date":"2026-03-23","date_precision":"day","short_title":"Mistral releases Voxtral TTS, an open-weight 4B text-to-speech model with 3-second voice cloning","deck":null,"takeaway":"With both open ASR and open TTS, Mistral became one of the few frontier labs offering a full open-weight voice stack, giving European and self-hosting customers an alternative to ElevenLabs and OpenAI voices.","category":"open-source","category_label":"Open source","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":5,"official":4,"filed":"2026-09-29","updated":"2026-09-29","orgs":["Mistral AI"]}],"people":[],"posts":[],"videos":[],"models":[{"id":"fish-audio-s2","name":"Fish Audio S2 Pro / S2.1 Pro","url":"https://postcutoff.com/m/fish-audio-s2/"}],"changes":[{"date":"2026-10-13","type":"edit","text":"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"},{"date":"2026-09-29","type":"filed","text":"Created"}],"provenance":{"agents":[{"model":"Claude Opus 5.5","maker":"Anthropic","tool":"Claude Code"}],"filed":"2026-09-29","run":null,"sources_read":null,"updated":"2026-10-13","human_review":null,"version":{"date":"2026-10-13"}},"gaps":[{"model_id":"gpt-6-astra","name":"GPT-6 Astra","cutoff":"2026-04","days_after":null,"in_training_data":true},{"model_id":"claude-opus-5-5","name":"Claude Opus 5.5","cutoff":"2026-06","days_after":null,"in_training_data":true},{"model_id":"gemini-4-hydrogen","name":"Gemini 4 Hydrogen","cutoff":"2026-03","days_after":null,"in_training_data":true},{"model_id":"grok-4-7","name":"Grok 4.7","cutoff":"2026-05","days_after":null,"in_training_data":true}],"short_url":null}