Fish Audio S2.1 Pro: The Free TTS Model That's Changing the Voice AI Game
If you've been building voice agents, audiobooks, dubbing tools, or any kind of AI voiceover product, you've probably run into the same wall everyone does: the good text-to-speech models cost money, and the free tiers are basically trial versions that run out in minutes. ElevenLabs gives you a few thousand credits and then the paywall hits. OpenAI's TTS has no free tier at all. Google's Gemini TTS charges from the very first token.
Fish Audio just flipped that script with S2.1 Pro — and the best part, right now you can use it completely free inside Celo AI, no charges till September 18th.
What Exactly Is S2.1 Pro?
S2.1 Pro is Fish Audio's current flagship voice model — a neural speech synthesis system built for production-grade AI voice generation. It's the upgraded version of their earlier S2 Pro model, and it's tuned specifically for three things: low-latency streaming, multilingual coverage, and voice cloning.
In plain Hinglish terms — yeh ek aisa TTS model hai jo bilkul insaan jaisi awaaz generate karta hai, real-time mein, aur wo bhi 83 languages mein.
The Numbers That Matter
Fish Audio didn't just tweak the old model — they rebuilt the inference stack from scratch. Here's what changed:
- ~70ms Time-to-First-Audio (TTFA) on a single request — down from ~100ms in the previous generation. That's fast enough for natural back-and-forth conversation, not just narration.
- 61% win rate against the older S2 Pro in blind listening evaluations.
- 2x+ throughput improvement under high-concurrency load, which matters a lot if you're building something that needs to serve multiple users at once.
- 83 languages supported, including English, Hindi, Japanese, Chinese, Korean, Spanish, Arabic, French, German, Portuguese, Russian, and dozens more — with automatic language detection, so you don't even need to specify what language the text is in.
What Makes It Stand Out From the Crowd
1. Natural language emotion control. Instead of being locked into a fixed set of emotion tags, S2.1 Pro uses bracket-based cues like [whispers sweetly] or [laughing nervously] directly inside your text. You're not choosing from a dropdown — you're describing the performance you want, and the model delivers it.
2. Zero-shot voice cloning. Give it a short reference clip, and it can replicate that voice across all 83 supported languages, keeping the same voice identity consistent no matter what language the text is in.
3. Multi-speaker synthesis in one call. You can generate dialogue between multiple voices in a single API call — genuinely useful if you're producing podcasts, audiobooks with multiple characters, or dubbed content.
4. Built for real conversation, not just narration. Most TTS models were designed for scripted, one-directional narration. S2.1 Pro is architected around real-time, turn-taking conversation — which is exactly what you need for voice agents and support bots.
Where This Actually Helps You
- Voice agents and chatbots — low latency means the conversation doesn't feel laggy or robotic.
- Audiobook and podcast production — multi-speaker support and emotional range cut down on manual editing.
- Localization and dubbing — 83-language coverage with consistent voice identity means one voice can carry your content across markets.
- Prototyping voice products — because it's free with no hard usage cap, you can actually stress-test an idea before committing budget to it.
- Content creators — Hinglish, regional Indian languages, and international content, sab kuch ek hi model se ban sakta hai.
Free on Celo AI Till September 18th
Yahan pe sabse badi baat: Celo AI par S2.1 Pro abhi free mein available hai, September 18th tak. Agar aap voice content, dubbing, ya AI-powered voiceovers try karna chahte ho bina kisi paid subscription ke, toh yeh window use karne ka best time hai.
Whether you're testing it for a client project, building a prototype, or just experimenting with AI voiceovers for your content — get in before the free window closes on September 18th.
Bottom Line
S2.1 Pro isn't a stripped-down "free tier" version of a paid product — it's the same state-of-the-art model running on both the free and paid API. That's rare in this space, and it's exactly why it's worth trying now while it's accessible on Celo AI at zero cost.
If you're serious about voice AI — narration, agents, dubbing, or cloning — this is a model worth putting through its paces before the free access window ends.