Fish Audio S2
UnclaimedThe most expressive open-source voice AI model for realistic and conversational speech generation.
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What is Fish Audio S2?
Fish Audio S2 (ai voice): The most expressive open-source voice AI model for realistic and conversational speech generation. Fish Audio S2 is an advanced, open-source text-to-speech (TTS) model designed for unparalleled expressiveness, speed, and flexibility. It allows users to generate highly realistic and natural-sounding speech with fine-grained control over emotions, paralanguage, and multi-speaker conversations. Key capabilities: Ultra-low latency speech generation (<150ms), Open domain control for emotions and paralanguage via natural text instructions, Multi-speaker conversations with seamless speaker switching, Fully open-source inference code and model weights, Support for 80+ languages. Fish Audio S2 ships a free plan plus paid tiers that unlock as usage grows. Buyers most often compare Fish Audio S2 against ElevenLabs, Listnr, Fliki.
TL;DR - Fish Audio S2
- Generates highly expressive and realistic speech with fine-grained control over emotion and paralanguage.
- Features ultra-low latency (<150ms) for real-time conversational AI and interactive applications.
- Fully open-source model weights and inference code, supporting 80+ languages and custom fine-tuning.
Pricing: Free plan available
Best for: Growing teams
Pros & Cons
Pros
- Exceptional expressiveness and realism in generated speech
- Open-source nature allows for self-hosting, fine-tuning, and integration flexibility
- Low latency makes it ideal for real-time and interactive voice applications
- Extensive language support (80+ languages)
- Detailed control over speech characteristics through natural language tags
Cons
- Commercial use requires a separate license, which might be a barrier for some businesses
- The free tier has significant limitations on generation time and character count
- Advanced features like fine-tuning require technical expertise to implement
Ratings Across the Web
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Preview
Key Features
Ultra-low latency speech generation (<150ms)Open domain control for emotions and paralanguage via natural text instructionsMulti-speaker conversations with seamless speaker switchingFully open-source inference code and model weightsSupport for 80+ languagesFine-grained inline control using natural language tags (e.g., [whisper], [emphasis])API access for integrationSGLang-based streaming inference engine for optimized performance
Pricing
Freemium
Fish Audio S2 offers a generous free tier with optional paid upgrades for advanced features.
About Fish Audio S2
By Toolradar Team·
Fish Audio S2 is an advanced, open-source text-to-speech (TTS) model designed for unparalleled expressiveness, speed, and flexibility. It allows users to generate highly realistic and natural-sounding speech with fine-grained control over emotions, paralanguage, and multi-speaker conversations. Built from the ground up for real-time applications, S2 boasts ultra-low latency, making it suitable for conversational AI, live dubbing, and interactive voice experiences.
The model supports localized control over speech generation through natural language instructions embedded directly within the text, enabling users to add elements like laughter, whispers, sighs, and specific tones. With full open-source access to both inference code and model weights, developers can run S2 on their own infrastructure, fine-tune it with custom data, and integrate it without vendor lock-in. It supports over 80 languages and is built with an SGLang-based streaming inference engine for optimized performance.
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Fish Audio S2 FAQ
What is the underlying architecture of Fish Audio S2 Pro and how does it achieve its expressiveness?
Fish Audio S2 Pro is built on a Dual-Autoregressive (Dual-AR) architecture, combining a 4B-parameter Slow AR for semantic prediction and a 400M-parameter Fast AR for acoustic detail. It's trained on over 10M+ hours of audio data across 80+ languages and uses reinforcement learning alignment to achieve its fine-grained prosody and emotion control.
How does Fish Audio S2 Pro's streaming performance compare to other TTS models?
On a single NVIDIA H200 GPU, S2 Pro achieves a Real-Time Factor (RTF) of 0.195, a time-to-first-audio of approximately 100ms, and a throughput of over 3,000 acoustic tokens per second, while maintaining RTF below 0.5. Its SGLang-based inference engine incorporates LLM-native serving optimizations like continuous batching and paged KV cache.
What is the difference between Tier 1 and Tier 2 languages supported by S2 Pro?
Tier 1 languages, such as Japanese, English, and Chinese, offer the highest quality speech generation. Tier 2 languages, including Korean, Spanish, Portuguese, Arabic, Russian, French, and German, also provide support, with many additional languages available.
Can I use Fish Audio S2 Pro for commercial projects if I'm using the open-source model weights?
The S2 Pro model is licensed under the Fish Audio Research License, which permits research and non-commercial use free of charge. Commercial use requires a separate license directly from Fish Audio.
How are credits calculated for speech generation on Fish Audio's platform?
Each minute of speech generation costs approximately 600 to 625 credits. These credits are replenished and reset monthly, and any unused credits do not roll over to the next billing cycle.
Source: fish.audio