Microsoft is opening WinUI development to public repositories while launching the open-source UI Reactor project, signalling a deeper commitment to community-driven native Windows development and faster Windows 11 experiences.
Microsoft has announced a major expansion of its open-source strategy for WinUI, moving the Windows UI framework towards more transparent, community-driven development as it rewrites key Windows 11 components in native code.
The company said WinUI has reached “Phase 3” of its open-source journey, allowing developers to build, test and validate changes publicly. Microsoft’s next goal, “Phase 4”, would see development occur primarily in public repositories, enabling external contributors to track changes, submit fixes and help shape the framework’s future.
Microsoft also introduced Microsoft UI Reactor, an experimental open-source, C#-first declarative UI framework designed to simplify native WinUI application development. The project removes dependencies on XAML, data binding and view models while introducing modern concepts such as hooks, state management and flex layouts. Successful innovations from Reactor are expected to migrate into production WinUI.
The open-source push accompanies Microsoft’s broader effort to rebuild Windows 11 around native technologies. Core shell components, including parts of the Start menu currently powered by React Native, are being rewritten using WinUI to improve responsiveness, reduce RAM and CPU usage, and enhance overall performance.
“We’ve started to integrate it into the shell at a much faster rate. And so you’re going to see a lot of the first-party features coming from Microsoft being built on top of WinUI,” said Chris Anderson, Vice President of Software Engineering at Microsoft.
Microsoft has also dropped the “3” from WinUI 3, reaffirming WinUI as its long-term native application platform with no plans for a future WinUI 4 framework.
