Windows 8 CD key for Windows 10
Windows 8 CD key for Windows 10
Learn how to upgrade your Windows 10 using Microsoft's free assistance features.
It’s essentially the final option to obtain it before they fully discontinue it.
I've applied a Windows 7 license to a Windows 10 setup this summer and it functions properly. The December 31 might relate to an assistive technology update within Windows. Simply transfer the Windows 10 USB drive and input the Windows 7 key during installation.
You haven't upgraded Windows 8 to 10 using the correct license. That means you have an older key, not compatible with the newer version. Microsoft stopped supporting upgrades from W7 through 10 a long time ago.
Your previous setup was a factory-installed version of Windows 8. The current key won’t function on a new system. You’ll need a retail copy of Windows 8 or 7 to use it. You can attempt this.
There exists a vulnerability, though accessing it may be viewed as copyright infringement.
Not exactly what you expect from Microsoft's official site, and it seems the response got a lot of attention when I submitted the question.