Microsoft shares new details about open-sourcing Windows 11's UI

At the beginning of this month, Microsoft revealed details about open-sourcing WinUI, Windows 11's user interface framework. Open-sourcing WinUI has been a long-standing request from developers, but implementing it is not as easy as flicking a single switch. Since WinUI has "deep roots" in proprietary levels of the operating system, opening the framework requires a careful and well-considered approach. A few weeks after the initial announcement, Microsoft is ready to share more information about the WinUI OSS project.

Microsoft wants to approach the task with four phases. Phase 1 is all about making more internal contributions available on GitHub. Phase 2 will let developers clone the repository and build WinUI locally. Phase 3 will allow third-party developers to contribute to the project, and the final phase will have GitHub as "the primary place for development, issue tracking, and community engagement," with internal repositories phased out.

Right now, developers at Microsoft are busy "untangling" WinUI from proprietary parts of Windows that cannot be shared publicly. Once Windows App SDK 1.8 is out later this month (currently in preview, and WinUI is tied to WASDK), developers will start implementing pull requests on GitHub. Microsoft plans to complete phase 1 by early October 2025.

As for allowing third-party devs to clone the repo and build locally, Microsoft says it is currently in "active exploration" of the idea. It requires a more cautious approach, so expect the company to take some time before sharing more details. Here is what the company says:

Because WinUI’s shipping schedule is tied to the Windows App SDK, our branching strategy now lets us start completing PRs alongside the upcoming WASDK 1.8 release. The 1.8 Preview shipped on August 19, and the stable release is coming soon, which gives us the right foundation to begin integrating changes. With that alignment, we’re targeting early October for completion of Phase 1.

 

Phase 2 is still in active exploration, and while we’re treating it more cautiously, we hope to share tangible progress soon.

You can follow the discussion about making WinUI open-source on GitHub.

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Posted Tuesday 26 August 2025 at 6:00 am AEST (my time).

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