This article (https://www.quora.com/Has-Windows-10-validated-the-privacy-warnings-of-Richard-Stallman-about-commercial-and-closed-source-operating-systems) suggests that Microsoft is releasing all it's source code. From what I can see they are only releasing information for hardware drivers which is a far cry from releasing the Microsoft Windows 10 source code. At least that is all I have seen on Gitjub so far. So do not get your hopes up.
The FSF aka Freedom Software Foundation released this video about the importance of having access to source code.
More information: https://www.fsf.org/blogs/community/user-liberation-watch-and-share-our-new-video#info