Microsoft has released the preview build 14366 for the Windows 10 Anniversary Update SDK. It will help app developers get ready for the final release of the Anniversary Update later this summer.
In a blog post, Microsoft stated:
The Preview SDK is a pre-release and cannot be used in a production environment. Please only install the SDK on your test machine. The Preview SDK Build 14366 contains bug fixes and under development changes to the API surface area. If you are working on an application that you need to submit to the store, you should not install the preview.
Microsoft has yet to reveal a specific release date for the Windows 10 Anniversary Update, but it is expected to go live sometime in late July for Windows 10, Windows 10 Mobile and the Xbox One.