Now today itself Microsoft has released a new updated SDK for Windows 10 build 14366 for developers. So that they can test their apps and games on this build before official release of Anniversary update which is due in somewhere around late July. Company has not declared release date for Anniversary update yet.
The blog post reads
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.