Thesys (thesys.dev) announced OUI-1 on September 8, 2026, calling it the first open-weights model built specifically for generative UI. It fine-tunes DiffusionGemma (26B total / 4B active parameters) to write output in openui-lang, Thesys's compact component-tree format, via supervised fine-tuning followed by rejection-sampled self-distillation. Weights are published on Hugging Face under the Gemma Terms of Use, not a fully permissive open-source license. It scores 71.7% on Thesys's own Generative UI Bench, ahead of Gemma 4 31B (46.7%) but behind Qwen3.8 27B (78.8%), with measured generation latency around 1.9 seconds.