> ## 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.

# Model Migration

To continue improving model quality and service reliability, the following models will be retired on **August 12, 2026**. After retirement, these models will stop serving inference requests, and applications that still call them will no longer receive valid responses.

<Warning>
  Please complete your model replacement, parameter tuning, and full end-to-end validation before **August 12, 2026** to keep your production services running.
</Warning>

## Retired models and recommended replacements

The table below lists the models being retired and the recommended replacement for each. In most cases, migrating means replacing the `model` field in your request with the replacement model ID.

| Model being retired | Recommended replacement                                    |
| ------------------- | ---------------------------------------------------------- |
| `step-tts-2`        | [`stepaudio-2.5-tts`](/docs/en/guides/models/stepaudio-2.5-tts) |
| `step-asr`          | [`stepaudio-2.5-asr`](/docs/en/guides/models/stepaudio-2.5-asr) |

<Note>
  `step-tts-2` and `stepaudio-2.5-tts` use different control paradigms: `step-tts-2` is tag-based (preset emotions and styles), while `stepaudio-2.5-tts` is controlled with natural-language context. Review how you specify delivery instead of only swapping the model ID. If you use cloned voices created with `step-tts-2`, validate them against `stepaudio-2.5-tts` and re-clone them if needed — see [Voice cloning](/docs/en/api-reference/audio/create-voice).
</Note>

## How to migrate

1. Find the model you currently use in the table above and note its recommended replacement.
2. Replace the `model` field value in your API requests with the replacement model ID — for example, change `step-tts-2` to `stepaudio-2.5-tts`.
3. Review the replacement model's capabilities on its model page (linked above) and its rates on [Pricing & Rate Limits](/docs/en/guides/pricing/details). We recommend running full validation before switching production traffic.

If you have questions, see the [FAQ](/docs/en/faq/common-questions).