Microsoft will no longer publish keys for Windows 10
Microsoft has changed the method of activation of the classical insider build of Windows 10, released after the version 10240. This applies to the already released Assembly 10525 and all others who come after her.
Answering a user’s question about whether the available product keys for activating new versions of Windows 10 Insider Preview, Gabe Ol from Microsoft gave a negative answer.
@viceroy101 No builds from here on will not be prekeyed or include keys. You can install on a PC that had an activated 10240 to activate.
— Gabriel Aul (@GabeAul) 22 Aug 2015
Now Insider Preview builds will be activated when you upgrade the computer on which you previously installed the public version of the operating system. In other words, if you have activated the final version and you update it to 10525 or more new pre-Assembly, the system is activated automatically when you first connect to your Microsoft account. To activate Windows 10, which was installed from scratch, you’ll need a retail product key.