How
Generation API/SDK: the model outputs UI as OpenUI Lang (or C1 responses) that a client renders; no live control channel.
Thesys C1 (now OpenUI Cloud) and OpenUI
Hosted generative-UI API plus open compact UI language.
thesys.dev ↗repo ↗docs ↗OpenUI Cloud (formerly C1 API) ↗OpenUI playground ↗
- license
- MIT · OpenUI (framework, OpenUI Lang, renderers) is MIT. C1 / OpenUI Cloud and OpenUI Gateway are proprietary hosted services.
- language
- TypeScript
- backing
- Thesys (company); funding not verified
- stars
- 10,546 (as of 2026-10-09)
- downloads
- @openuidev/react-lang 135,398/week (npm, week ending 2026-10-07); site claims 642,626/month
- latest release
- @openuidev/react-lang 0.3.2, 2026-10-08
- first release
- 2026-03
ignore
A web generation service; only its compact-language token-cost lesson applies to scene.
Ignore it for this purpose.
the steelman: the best honest case for it
Thesys attacks the real cost of generative UI: tokens and latency. OpenUI Lang is a purpose-built compact language that, by its own reproducible tiktoken benchmark, needs roughly half to a third of the tokens of json-render or C1's own old JSON, which means faster first paint and cheaper turns. The framework is MIT, renders in four web frameworks, interoperates with A2UI and AG-UI, and the hosted OpenUI Cloud adds the unglamorous production parts (validation, correction, fallbacks, model gateway, observability) teams otherwise build themselves.
scores
| UI as data | 4 scene 5 | OpenUI Lang is a serializable text format, but not JSON. |
|---|---|---|
| Agent can drive it | 2 scene 5 | More than code generation (constrained DSL rendered safely) but no protocol to change a live instance. |
| Agent can see it | 1 scene 5 | No readback mechanism found in docs reviewed. |
| Small, targeted edits | 1 scene 5 | |
| Time travel | 0 scene 0 | |
| Live data rate | 1 scene 5 | |
| Terminal native | 0 scene 5 | |
| Pixel graphics | 3 scene 4 | Web charts and components. |
| Teaching | 0 scene 3 | |
| Maturity | 3 scene 1 | |
| Openness | 3 scene 4 | MIT framework, proprietary hosted API. |
Thesys C1 (now OpenUI Cloud) and OpenUI scene now scene planned
how agents use it
Wiring it in
Low for web apps: swap the LLM endpoint (C1) or add the OpenUI renderer and prompt.
Seeing the result
Not documented beyond normal chat/app state (not verified).
Small edits
Not documented; responses are regenerated per turn (not verified).
History
None documented.
In short
Optimised for cheap, fast generation of web UI, not for operating a live interface.
architecture
C1 was an OpenAI-compatible LLM API that returns UI (charts, forms, tables, cards) instead of text, rendered by Thesys's React SDK. It is now 'OpenUI Cloud', built on the open OpenUI framework: developers define a component library (Zod-typed), generate a system prompt from it, the model streams OpenUI Lang (a compact text language, not JSON), and React/Vue/Svelte/Angular renderers draw it progressively. @openuidev/a2ui offers an A2UI v1.0 client with OpenUI Lang component payloads; @openuidev/langchain streams OpenUI through AG-UI.
- OpenUI Lang: compact, streaming-first, claims up to 67% fewer tokens than JSON formats
- Library-driven prompts and controlled rendering (only registered components)
- Hosted extras: validation/correction/fallback, gateway across models, observability
- No terminal renderer
performance
Token benchmark is published in the repo (reproducible); render-speed and user-preference claims are marketing without published method.
- OpenUI Lang uses 55-67% fewer tokens than Vercel json-render and Thesys C1 JSON across seven scenarios (tiktoken, GPT-5 encoder) github.com ↗
- 3x faster renders compared to JSON renderers thesys.dev ↗
adoption and upkeep
Adoption
Commercial generative-UI API rebranded as OpenUI Cloud, with an open-source OpenUI framework that is growing quickly (10.5k stars).
Used by: Entelligence (Ask Ellie), per thesys.dev, CTRLAgent, FieldCamp (logos on thesys.dev)
Maintainability
Active open-source repo backed by a commercial product.
Releases: Frequent package releases (five packages released 2026-10-08) · Contributors: ~50 (GitHub contributors API incl. anonymous) · Recent: 361 commits on main since 2026-07-11 (GitHub API) · Bus factor: medium: one company
weaknesses
- C1 itself is a proprietary SaaS; the brand has shifted (C1 -> OpenUI Cloud), so 'C1' docs and APIs may move
- Another UI dialect (OpenUI Lang) beside A2UI and json-render
- Web-only; no terminal renderer
- No readback, patching or history for agents (not documented)
- Customer list and performance claims beyond the token benchmark are marketing
and thc-scene
Overlap
Agent-generated UI constrained to a trusted component library.
What scene would be reinventing
Little; scene does not target model-generated UI token cost.
The gap it leaves
Terminal rendering, live control, readback, data streams bypassing the model, pixels, history.
What to borrow
- A compact text form for agent-written scenes to cut tokens (the token benchmark is a useful yardstick)
- Prompt generation from the component library
sources
- Thesys homepage (OpenUI Cloud, formerly C1 API) thesys.dev
- thesysdev/openui README (token benchmark) github.com
- npm downloads API api.npmjs.org