Rendel vs Thesys: an assistant for your app, or a generative UI API to build one
Thesys OpenUI facts read on 12 October 2026 from Thesys OpenUI’s own pages, rechecked every 90 days
Choose Thesys if you are building your own AI product on the web and want model output rendered as UI. Choose Rendel if you want an assistant inside your existing app that answers with your components and runs your actions after the user confirms.
Side by side
- What it is
- RendelA complete in-app assistant: SDK, API and console
- Thesys OpenUIA hosted Generative UI API (OpenUI Cloud, formerly the C1 API) (thesys.dev)
- Platforms
- RendelFlutter apps on iOS and Android, and any website. Native iOS, native Android and React Native are planned, not shipped.
- Thesys OpenUIReact, Vue, Svelte and Angular runtimes (github.com)
- Pricing
- RendelPilot free; Starter $199 and Growth $799 a month with usage credit included; Enterprise by contract.
- Thesys OpenUIFree to $499 a month by API calls; model tokens billed separately (thesys.dev)
Where Thesys OpenUI is the better choice
- Model-agnostic; you bring your own model.
- Open-source framework (MIT) for the rendering.
Where Rendel fits
- Your app is in Flutter.
- You want your actions, confirmation and a console, not only rendering.
Sources
- OpenUI Cloud was formerly the C1 API. thesys.dev
- Plans are $0, $49 and $499 a month by API calls; LLM tokens are billed separately. thesys.dev
Questions
Which model does Rendel use?
Anthropic's Claude, a fast model for quick turns and a larger one for the rest. You do not manage a model.