S2 Pro
S2 Pro is Fish Audio's open-source text-to-speech model covering 80+ languages, with natural language prosody control and multi-speaker dialogue in a single request.
- Price
- Free
import { experimental_generateSpeech as generateSpeech } from 'ai';import { gateway } from '@ai-sdk/gateway';import { writeFile } from 'node:fs/promises';
const result = await generateSpeech({ model: gateway.speechModel('fish-audio/s2-pro'), text: 'Hello from the Vercel AI Gateway!', // Browse voices at https://fish.audio/app/discovery // Open a voice, then use "Copy Model Id" in its "..." menu. voice: '933563129e564b19a115bedd57b7406a',});
await writeFile('speech.mp3', result.audio.uint8Array);Copy link to headingPlayground
Try out S2 Pro by Fish Audio. Usage is billed to your team at API rates. Free users (those who haven't made a payment) get $5 of credits every 30 days.
S2 Pro
Your generated audio will appear here
Copy link to headingProviders
Route requests across multiple providers. Copy a provider slug to set your preference. Visit the docs for more info. Using a provider means you agree to their terms, listed under Legal.
| Provider |
|---|
Fish Audio Legal:Terms•PrivacyFree | Free | 03/09/2026 |
Copy link to headingMore models by Fish Audio
| Model |
|---|
| — | Free | Free | — | | 07/28/2026 | |||||||||
| — | Free | Free | — | | 03/01/2026 | |||||||||
| — | Free | Free | — | | 10/20/2025 |
Copy link to headingAbout S2 Pro
S2 Pro is Fish Audio's open-source text-to-speech model, covering more than 80 languages. The release includes the model weights, fine-tuning code, and a complete serving stack, which is what separates it from the hosted-only options in the family.
The architecture is a dual autoregressive design over a residual vector-quantized audio codec. A larger model predicts the primary semantic codebook and a smaller one fills in the remaining residual codebooks at each step, which is how it keeps quality high without running one large model over every codebook.
Prosody control works the same way as in the S2.1 generation. Direction is written inline in square brackets and interpreted as description rather than matched against a fixed vocabulary, so arbitrary phrasing works. Multi-speaker dialogue is supported in a single request.
Integration uses the AI SDK's speech generation function.
Copy link to headingWhat To Consider When Choosing a Provider
- Configuration: The licence is the thing to check first. S2 Pro is published under Fish Audio's research licence: research and non-commercial use is free, and commercial use requires a separate licence agreement. Open weights here do not mean open commercial rights.
- Configuration: S2.1 Pro supersedes this model. It covers three more languages, and listening comparisons favour it, so choose S2 Pro when you specifically want published weights or a self-hosted serving stack, and S2.1 Pro when you want the best available quality through an API.
- Configuration: Self-hosting means operating the serving stack yourself. Through AI Gateway you skip that, but then the open weights are not the reason you are choosing this model, and S2.1 Pro is likely the better pick.
- Zero Data Retention: Zero Data Retention is offered on a per-provider and model basis. See the documentation for details.
- Authentication: AI Gateway authenticates requests using an API key or OIDC token. You do not need to manage provider credentials directly.
Copy link to headingWhen to Use S2 Pro
Best for
- Open-Weight Voice Work: Published weights and fine-tuning code
- Self-Hosted Serving: A released inference stack you can operate
- Multilingual Coverage: More than 80 languages
- Expressive Direction: Plain-language control rather than a fixed tag list
- Custom Fine-Tuning: A published base to build on
Consider alternatives when
- Commercial Use: Requires a separate licence agreement from Fish Audio
- Best Available Quality: S2.1 Pro wins head-to-head listening comparisons
- Maximum Language Coverage: S2.1 Pro supports three more languages
- Hosted-Only Deployments: Open weights bring no benefit if you never self-host
Copy link to headingConclusion
S2 Pro is the open-source generation of Fish Audio's voice models, with published weights, a serving stack, and 80+ language coverage. Point fish-audio/s2-pro at AI Gateway to try it, and read the research licence before any commercial deployment.
Copy link to headingFrequently Asked Questions
Is S2 Pro open source?
The weights, fine-tuning code, and serving stack are published, but under Fish Audio's research licence. Research and non-commercial use is free; commercial use requires a separate licence.
How many languages does S2 Pro support?
More than 80. S2.1 Pro extends that to 83.
How is S2 Pro different from S2.1 Pro?
S2.1 Pro is the improved successor, with better quality, latency, and throughput, and it wins head-to-head listening comparisons. Choose S2 Pro when published weights or self-hosting is the requirement.
How do I control emotion and delivery?
Write direction inline in square brackets. The model interprets the description rather than matching a fixed tag list, so phrasing outside any documented set still works.
Can S2 Pro render dialogue?
Yes. Multi-speaker dialogue is supported in a single request, with each turn tagged by speaker index.
Does S2 Pro support Zero Data Retention?
Zero Data Retention is not currently available for this model. Zero Data Retention is offered on a per-provider basis. See https://vercel.com/docs/ai-gateway/capabilities/zdr for details.
Your use is subject to Fish Audio's Terms & Privacy Policies.