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.
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!' }
]
})


Traditional apps had fixed paths, so their UIs were hardcoded. AI unlocks infinite user journeys.
We built C1 so that the UI can keep up.
C1 by Thesys is a Generative UI API that lets you build AI-powered applications with interfaces that generate themselves - based on user input, context, or intent - instead of being hardcoded.
It's an OpenAI-compatible endpoint that returns structured UI components like forms, visualizations and layouts instead of markdown. The output is then parsed by the React SDK to create the UI.
You prompt it like a chat completion API-and it responds with live, usable UI.
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, we currently support Anthropic models and are planning to add support for more LLMs, including OpenAI, soon to give developers even more flexibility.
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.