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

# C1 by Thesys documentation (archive)

> The C1 documentation, kept online for teams already running C1 in production. New projects should start with the OpenUI docs.

C1 documentation now lives here, under `/legacy`. Everything that used to be at
`docs.thesys.dev/<page>` is served at `docs.thesys.dev/legacy/<page>`, and the old URLs
redirect to the [OpenUI docs](https://www.openui.com/docs).

<Card title="Building something new?" icon="arrow-right" href="https://www.openui.com/docs" horizontal>
  OpenUI is the actively developed successor to C1. Start there.
</Card>

## If you already run C1

C1 and its APIs keep working, and these pages keep describing them. Nothing here is being
removed — it is just no longer the default entry point.

* [Setup](/legacy/guides/setup) — install the SDK and call the C1 API
* [API reference](/legacy/api-reference/getting-started) — endpoints, models, rate limits, errors
* [React reference](/legacy/react-reference/c1-component) — `C1Component`, `C1Chat`, `ThemeProvider`
* [Agent Builder](/legacy/agent-builder/introduction) — embed widget and BYOI
* [Troubleshooting](/legacy/support/troubleshooting)

## Moving to OpenUI

The [OpenUI migration guide](https://www.openui.com/docs/agent/guides/migrating) maps the old
component props onto `AgentInterface`. For questions specific to your setup,
[talk to us](mailto:support@thesys.dev) or ask in [Discord](https://discord.gg/Pbv5PsqUSv).