Build 2020: Microsoft announces Project Reunion to unify Win32 and UWP


Build 2020: Microsoft announces Project Reunion to unify Win32 and UWP

Recently, Microsoft has kicked off its online event Build 2020 Developer Conference. At Build 2020, the company has announced Project Reunion, which aims to unify the UWP (Universal Windows Platform) and Win32. 

Image: Microsoft

It’s been years since the company has been encouraging developers to use the new UWP for building Windows apps instead of Win32. With this Project Reunion, all the apps will be just Windows Apps – there will be no Win32 or modern universal app. Here is what Microsoft mentioned about it:

For the past couple of years, we have been breaking down the barrier between Win32 (also called the Windows API) and Universal Windows Platform (UWP) APIs. Project Reunion expands this effort to make it easier to build a great Windows app. It will unify access to existing Win32 and UWP APIs and make them available decoupled from the OS, via tools like NuGet. This will provide a common platform for new apps. Plus, it will help you update and modernize your existing apps with the latest functionality, whether they’re C++, .NET (including WPF, Windows Forms, and UWP) or React Native. As we decouple existing APIs and add new APIs, we are also doing the work to polyfill, as needed, so the APIs work down-level across supported versions of Windows.

This project will unify the existing Win32, and UWP APIs and developers can use them from NuGet. APIs like WinUI 3WebView2, and MSIX (MSIX-Core) are already part of the project and are available for developers. The company also confirms that the new apps developed by this will support all versions of Windows 10.

Project Reunion Principles


Project Reunion works in all your apps – Win32, Packaged, and UWP – and across many versions of Windows.


Project Reunion supports your app’s use of modern software libraries for UI, AI, ML, packaging, frameworks, and libraries. Language projections for C++, Rust, C#, and JavaScript expand the benefits to all your apps. Cloud-backed apps, streaming, and edge-compute apps are all great places to use Project Reunion’s capabilities.


Project Reunion ships out of band with OS releases, with regular previews. You get to incrementally adopt Project Reunion components for your existing apps and middleware libraries using NuGet.


We’re committing to engineering Project Reunion in the open on GitHub, so you have a more direct say in how the platform evolves and can even help out.

Thus, its an effort to streamline the idea that is anything running on Windows 10 is Windows app. And soon, users will be unable to differentiate between UWP or Win32 apps if they are running on Windows 10.

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