Fish Audio S2 Technical Report
Authors: name: Shijia Liao, name: Yuxuan Wang, name: Songting Liu, name: Yifan Cheng, name: Ruoyi Zhang, name: Tianyu Li, name: Shidong Li, name: Yisheng Zheng, name: Xingwei Liu, name: Qingzheng Wang, name: Zhizhuo Zhou, name: Jiahua Liu, name: Xin Chen, name: Dawei Han
Organization: Fish Audio

We introduce Fish Audio S2, an open-sourced text-to-speech system featuring multi-speaker, multi-turn generation, and, most importantly, instruction-following control via natural-language descriptions. To scale training, we develop a multi-stage training recipe together with a staged data pipeline covering video captioning and speech captioning, voice-quality assessment, and reward modeling. To push the frontier of open-source TTS, we release our model weights, fine-tuning code, and an SGLang-based inference engine. The inference engine is production-ready for streaming, achieving an RTF of 0.195 and a time-to-first-audio below 100 ms.Our code and weights are available on GitHub (https://github.com/fishaudio/fish-speech) and Hugging Face (https://huggingface.co/fishaudio/s2-pro). We highly encourage readers to visit https://fish.audio to try custom voices.