Windows App SDK
Other namesProject Reunion
Initial release29 March 2021
Stable release
1.4.5[1] Edit this on Wikidata / 14 February 2024
Preview release
1.5-preview1[2] Edit this on Wikidata / 14 February 2024
Written inC++
Operating systemWindows 11, Windows 10 version 1809 and later
Platformx86-64, ARM64, IA-32
TypeApplication programming interface (API)
LicenseMIT License Edit this at Wikidata

Windows App SDK (formerly known as Project Reunion)[3] is a software development kit (SDK) from Microsoft that provides a unified set of APIs and components that can be used to develop desktop applications for both Windows 11 and Windows 10 version 1809 and later. The purpose of this project is to offer a decoupled implementation of capabilities which were previously tightly-coupled to the UWP app model.[4] Windows App SDK allows native Win32 (USER32/GDI32) or .NET (WPF/WinForms) developers alike a path forward to enhance their apps with modern features.[4]

It follows that Windows App SDK is not intended to replace the Windows SDK.[4] By exposing a common application programming interface (API) primarily using the Windows Runtime (WinRT) through generated WinMD metadata, the tradeoffs which once characterized either app model are largely eliminated. NuGet packages for version 1.4 were released in August 2023 after approximately four months of development.[5]

Features and components

While Microsoft has developed a number of new features, some of the features listed below are abstractions of functionality provided by existing APIs.[4]

WinUI 3

Most of the investment[6] into the decoupled UI stack[7] has gone towards bug fixes, improvements to the debugging experience, and simplifying the window management capabilities made possible by switching from CoreWindow. An API abstracting USER32/GDI32 primitives known as AppWindow was introduced to expose a unified set of windowing capabilities[8] and enable support for custom window controls.


A replacement for the UWP WebView control was announced early on.[9] This is because it was based on an unsupported browser engine.[10] A new Chromium-based control, named WebView2, was developed and can be used from WinUI as well as other supported app types.


While MSIX is included in the Windows App SDK and considered to be the recommended application packaging format,[11][12] a design goal was to allow for unpackaged apps. These apps can be deployed as self-contained or framework-dependent. Support for dynamic loading of app dependencies is included for both packaged and unpackaged apps.[13]


DWriteCore is being developed as a decoupled and device-independent solution for high-quality text rendering.[14] Win2D has also been made available to WinUI 3 apps.[15]

Resource management

MRT Core allows for management of app resources for purposes such as localization. It is a decoupled version of the resource management system from UWP.[16]

App lifecycle

With the stable releases delivered after its initial launch, Windows App SDK now supports several app lifecycle features which previously required a considerable amount of effort for developers to implement in Win32 applications. These features include power management notifications, rich activation, multiple instances, and programmatic app restart.[17]


Support for push notifications was initially implemented as a limited-access, preview feature.[18] However, the APIs for it have since been stabilized and push notifications can be delivered to app users. Official documentation states that access to the feature can be revoked by Microsoft at their discretion.[18][19] Additionally, apps can now easily display local app notifications without the need to create an XML payload.[20]


Third-party integration with the Windows Widgets system in Windows 11 has been included as part of the stable release channel.[21] Developers can design custom widgets for their app using adaptive cards[22] and surface them on the widgets board.[23]

See also


  1. ^ "Release 1.4.5". 14 February 2024. Retrieved 20 February 2024.
  2. ^ . 14 February 2024 Retrieved 3 March 2024. ((cite web)): Missing or empty |title= (help)
  3. ^ Ramel, David (June 24, 2021). "Windows 11 Development: Open Ecosystem Store, Project Reunion Rebrand and More". Visual Studio Magazine. Retrieved 2021-10-11.
  4. ^ a b c d Windows App SDK - Calling all Windows developers!, Microsoft, 2023-05-25, retrieved 2023-05-26
  5. ^ "Microsoft.WindowsAppSDK 1.4.230822000". Retrieved 2023-09-11.
  6. ^ "Release v1.3.0 · microsoft/WindowsAppSDK". GitHub. Retrieved 2023-05-26.
  7. ^ Karl-Bridge-Microsoft (2023-03-13). "Windows UI Library (WinUI) - Windows apps". Retrieved 2023-05-26.
  8. ^ "Discussion #370: Announcement: Proposed approach for windowing in Project Reunion". microsoft/WindowsAppSDK. GitHub. Retrieved 2022-04-19.
  9. ^ Blog, Microsoft Edge; Team, Microsoft Edge (2020-10-19). "Announcing Microsoft Edge WebView2 General Availability". Microsoft Edge Blog. Retrieved 2023-05-26.
  10. ^ "New Microsoft Edge to replace Microsoft Edge Legacy with April's Windows 10 Update Tuesday release". TECHCOMMUNITY.MICROSOFT.COM. 2021-02-10. Retrieved 2023-05-26.
  11. ^ dianmsft (2021-12-30). "What is MSIX? - MSIX". Retrieved 2023-05-26.
  12. ^ stevewhims (2023-03-03). "MSIX framework packages and dynamic dependencies - Windows apps". Retrieved 2023-05-26.
  13. ^ stevewhims (2023-04-19). "Use the Windows App SDK runtime for apps packaged with external location or unpackaged - Windows apps". Retrieved 2023-05-26.
  14. ^ stevewhims (2022-02-24). "DWriteCore (Windows App SDK) - Windows apps". Retrieved 2023-05-26.
  15. ^ stevewhims (2023-05-25). "Win2D - Windows apps". Retrieved 2023-05-26.
  16. ^ hickeys (2023-03-13). "Manage resources MRT Core (Windows App SDK) - Windows apps". Retrieved 2023-05-26.
  17. ^ hickeys (2023-01-31). "App lifecycle and system services - Windows apps". Retrieved 2023-05-26.
  18. ^ a b hickeys (2023-03-16). "Push notifications overview - Windows apps". Retrieved 2023-05-26.
  19. ^ hickeys (2022-06-03). "Notifications design basics - Windows apps". Retrieved 2023-05-26.
  20. ^ vaheeshta (2022-07-12). "App notifications overview - Windows apps". Retrieved 2023-05-26.
  21. ^ drewbatgit (2023-03-09). "Widget providers - Windows apps". Retrieved 2023-05-26.
  22. ^ drewbatgit (2022-11-10). "Create a widget template with the Adaptive Cards Designer - Windows apps". Retrieved 2023-05-26.
  23. ^ drewbatgit (2023-03-09). "Windows Widgets - Windows apps". Retrieved 2023-05-26.