> ## Documentation Index
> Fetch the complete documentation index at: https://platform.stepfun.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# FAQ

## Audio models

### What model should I use for text-to-speech?

For new projects, use `stepaudio-2.5-tts` — our flagship contextual TTS model with zero-shot voice cloning and natural-language control over emotion and style. Use `step-tts-2` if you rely on tag-based voice/emotion control or preset voice libraries. See [Audio Models](/en/guides/models/audio) for a full comparison.

### Where can I find the TTS API parameters?

See [Generate audio](/en/api-reference/audio/create-audio) for the full request schema and examples.

### What audio formats are supported?

`wav`, `mp3`, `flac`, `opus`, `pcm`. Default is `mp3`.

### Is there a limit on input length?

Yes. The maximum input length is 1,000 characters per request.