Thesys open-sources AppLess, its no-app phone demo, with OUI-1
The React Native experiment now uses a self-hosted diffusion model, though every booking, payment and order remains simulated.
By Ryan Merket · Published
Primary source: X - Rabi Shanker Guha
Why it matters
AppLess turns Thesys's generative UI thesis into a forkable stack, while exposing the remaining gap between drawing an interface and completing a real transaction.
Rabi Shanker Guha (@rabi_guha), co-founder and CEO of Thesys, said in a post on X on September 17th that AppLess now generates its interfaces with OUI-1 and that developers can download the components behind the no-app phone experiment.
https://x.com/rabi_guha/status/2100597151130910961
Guha founded Thesys with Parikshit Deshmukh in 2024 after leaving DevRev, where Guha had spent three years. Thesys has built around Guha's argument that AI software needs interfaces generated for each request, rather than another chat box attached to a fixed application. AppLess is the most literal demonstration of that thesis: users ask for something and receive a newly generated native screen instead of opening an installed app.
Thesys raised a $4 million seed round in November 2024. Together Fund led the round, with 8VC participating.
What developers can actually run
The AppLess repository contains an Expo and React Native client that renders the same generated interface with Cupertino components on iOS and Material 3 components on Android. A component contract defines the names, properties and descriptions available to the model. That contract becomes a system prompt, OUI-1 writes the screen in OpenUI Lang, and the OpenUI renderer turns the streamed output into native interface elements.
The phone does not run OUI-1 itself. Developers must serve the model through vLLM 0.24 or newer on a separate GPU host, then point AppLess at that server over an OpenAI-compatible endpoint. Thesys recommends FP8 weights, which occupy about 25.8 GiB before runtime and cache memory, and configures a 16,384-token context window.
That setup removes AppLess's previous dependence on Gemma 4 inference through Cerebras, while keeping substantial compute outside the handset. Thesys describes OUI-1 as suitable for consumer hardware, specifically an RTX 5090 at FP8. AppLess currently remains a phone client connected to a GPU server rather than an on-device model.
The OUI-1 weights contain 26 billion total parameters with 4 billion active for each token. OUI-1 is a fine-tune of Google's DiffusionGemma 26B-A4B-it. The diffusion architecture works on 256-token blocks, instead of generating each token sequentially, which Thesys is using to reduce the delay before a generated screen appears.
On Thesys's Generative UI Benchmark, OUI-1 completed 132 of 184 runs for a score of 71.7%, compared with 13% for the base DiffusionGemma model. Thesys has published the scoring protocol and raw outputs, allowing developers to rerun the validation. The comparison has a clear ceiling: Qwen3.8 27B scored 78.8%, though it activates 27 billion parameters for each token. On a separate 60-prompt test using the AppLess component library, Thesys reported 55 valid OUI-1 outputs, compared with 23 from DiffusionGemma.
The phone without apps still needs the apps' plumbing
AppLess can generate weather dashboards, restaurant lists, booking forms and message threads. Optional search and image integrations can ground the displayed information in live sources. The actions behind those screens remain simulated. An "order placed," "flight booked" or "payment sent" message does not call a merchant, airline or bank, and generated health readings do not reflect a connected device.
That limitation defines the engineering work AppLess is handing to outside developers. A generated interface can replace navigation and fixed screens only after someone connects authentication, state, payments and service APIs. Thesys is inviting developers to fork AppLess and add those integrations.
The release includes the MIT-licensed AppLess client and the MIT-licensed OpenUI framework. The description of the entire stack as open source needs qualification for OUI-1. Thesys's September 8th release post described the weights as Apache 2.0, while the current Hugging Face model card labels the license as "gemma" and says Google's Gemma terms and use restrictions apply. Developers planning redistribution or commercial deployments will need to follow the current model card and underlying license.
The open release also sits next to Thesys's paid infrastructure. OpenUI pricing lists managed Gateway plans that validate and repair generated interfaces, route between model providers and provide production controls. AppLess gives developers a conspicuous reason to adopt OpenUI Lang; Thesys sells the reliability layer required when those generated screens move beyond a demo.