Make AI apps respond with
C1 by Thesys is an API middleware that augments LLMs
to respond with interactive UI in realtime instead of text.
Open demo Experience Generative UI in action
Type a prompt or pick a suggestion to interact with demos built with C1 API
How C1 Works
C1 is an API layer on top of LLMs that builds adaptive UIs in real time. It turns responses from your model into live interfaces using our React SDK.
Integrate C1 in 3 easy steps
const { OpenAI } = require('openai')
// Create OpenAI client with Thesys endpoint
const client = new OpenAI({
apiKey: process.env.THESYS_API_KEY,
baseURL: 'https://api.thesys.dev/v1/embed'
})
// Now use the client for your AI requests
const response = await client.chat.completions.create({
model: '<model-name>',
messages: [
{ role: 'user', content: 'Hello, world!' }
]
})Built for AI-native teams
Ship AI experiences you can imagine - assistants, copilots, canvases, and more without any frontend overhead.
Built by Developers, for Developers
Zero overhead, fully flexible, giving developers total control.
Frequently
asked questions
Everything you need to know to get started.
C1 by Thesys is a LLM API that turns large language model (LLM) responses into live, adaptive user interfaces in real time.
Instead of returning plain text like traditional completion endpoints, C1 outputs structured UI components - such as forms, tables, charts, and layouts - that can be rendered directly using the C1 React SDK.
It supports multiple LLMs like OpenAI, Anthropic, & more, works out of the box or with your custom design system, and is built for fast, secure, and real-time rendering of dynamic interfaces.
With C1, developers can build intelligent, context-aware frontends for AI-powered apps - without hardcoding the UI for every possible user query or state.
Generative UI is for teams building AI-native software-agents, copilots, and tools-where use cases evolve fast, and static UIs fall short.
- Adapts to logic, state, and user behavior
- LLMs shape both output and interaction
Perfect for devs, product teams, and builders creating dynamic, task-specific interfaces.
Tools like Lovable or Bolt help you design UI before your app goes live-they turn prompts into mockups or code.
C1 by Thesys is different: it builds and shows the actual interface while the app is running, tailored to each user and situation. Think of it this way:
- Tools like Lovable or Bolt are coding assistants that help write the code that powers the UI.
- C1 is the UI - live, flexible, and ready when users need it.
Yes, C1 works with all leading LLMs out of the box, including models from Anthropic and OpenAI. We're continuously adding more to give you maximum flexibility to build, test, and scale without locking into a single provider.
Yes, C1 lets you customize the UI to match your companys design system.
It's built on top of Crayon's UI library, so any customization supported by Crayon - like themes, tokens, or components - works out of the box.