As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/m/fish-audio-s2/

# Fish Audio S2 Pro / S2.1 Pro

Fish Audio, Fish Audio S2 family. Status: current. Type: speech and audio. Released: 2026-03-09.

## How to call it

| Provider | Model id | Endpoint | Docs |
|---|---|---|---|
| Fish Audio API | `s2.1-pro` | https://api.fish.audio/v1/tts (model passed in `model` header) | https://docs.fish.audio/developer-guide/getting-started/changelog |
| Fish Audio API (free tier) | `s2.1-pro-free` | https://api.fish.audio/v1/tts |  |
| Fish Audio API | `s2-pro` |  |  |
| Hugging Face | `fishaudio/s2-pro` |  | https://huggingface.co/fishaudio/s2-pro |
| OpenRouter |  |  | https://openrouter.ai/fish-audio/s2.1-pro |
| GitHub |  |  | https://github.com/fishaudio/fish-speech |

## Pricing

- Per 1M UTF-8 bytes: $15
- Unit as published: USD per 1M UTF-8 bytes (s1, s2-pro, s2.1-pro); s2.1-pro-free $0 under fair use through 2026-11-30; ASR transcribe-1 $0.36/hr
- Source: https://docs.fish.audio/developer-guide/models-pricing/pricing-and-rate-limits
- Last checked: 2026-09-29

## Specs

- Input: text, audio
- Output: audio
- Context window: not published
- Max output: not published
- Open weights: yes
- Licence: Fish Audio Research License (S2 Pro weights; non-commercial, commercial license on request)

## Where it stands

- Newer speech and audio models in the registry since its release: 64. The 5 newest:
  - NVIDIA Nemotron 3.5 Transcribe (30B-A4B) (2026-10-28) https://postcutoff.com/m/nemotron-3-5-transcribe/
  - Hy-SimulMT-30B-A3B (2026-10-22) https://postcutoff.com/m/hy-simulmt-30b-a3b/
  - Eleven Realtime v1 Max / Mini (2026-10-20) https://postcutoff.com/m/eleven-realtime-v1-max/
  - Voxtral Mini Transcribe 3 (+ Mini Transcribe Realtime 3) (2026-10-20) https://postcutoff.com/m/voxtral-mini-transcribe-3/
  - Voxtral Small Transcribe 3 (2026-10-20) https://postcutoff.com/m/voxtral-small-transcribe-3/
- After it from Fish Audio: Fish Audio Drama 3 (2026-10-13) https://postcutoff.com/m/fish-audio-drama-3/
- Weights are public. Licence: Fish Audio Research License. See the licence for commercial terms.

## What stands out

- Inline natural-language emotion/paralinguistic tags: Free-form bracket cues like [whisper], [laugh], [emphasis]; multi-speaker dialogue in one pass; 80+ languages from 10M+ hours of training audio. Source: https://fish.audio/blog/fish-audio-open-sources-s2/
- Open model with production inference stack: Dual-AR (4B slow + 400M fast) on a Qwen3-4B backbone released with fine-tuning code and SGLang serving; RTF 0.195, ~100 ms TTFA; Seed-TTS Eval WER 0.54% zh / 0.99% en. Source: https://arxiv.org/abs/2603.08823
- Free production API (S2.1 Pro) (found after launch): S2.1 Pro (closed, 2026-06-23) offered free under fair use with ~90 ms TTFA, 83 languages; 61% win rate vs S2 Pro. Source: https://fish.audio/blog/s2-1-pro-free-api/

## Notes

S2 Pro held #1 open-weights on Artificial Analysis until Breeze TTS 2 (Aug 2026); now #2 open (~1119 Elo). S2.1 Pro weights are NOT open. OpenRouter lists S2.1 Pro release as 2026-07-29 (API availability there). Predecessor OpenAudio S1 (`s1`) is deprecated and retires 2026-12-31 (requests then served and billed as s2.1-pro). Successor: Drama 3 (2026-10-13, see fish-audio-drama-3); on Artificial Analysis S2 Pro is now the #3 open-weights model (Elo 1118, read 2026-10-13). The pricing page no longer shows an end date for s2.1-pro-free (read 2026-10-13).

Sources: https://docs.fish.audio/developer-guide/models-pricing/pricing-and-rate-limits , https://huggingface.co/fishaudio/s2-pro , https://fish.audio/blog/s2-1-pro-free-api/

Model page: https://postcutoff.com/m/fish-audio-s2/