Windows 10 will be offered free of charge to those who upgrade from Windows 7 or Windows 8.1, but since a genuine product key is automatically upgraded to Windows 10 once you complete the transition, many wondered whether a clean install is possible or not.
Microsoft has confirmed today, through the voice of Gabe Aul, head of the Windows Insider program, that clean installs will be possible for those who upgrade to Windows 10 for free from any of the supported Windows versions, but no other details have been provided.
He has mentioned that you will be able to clean install Windows 10 on that PC at any given time for as many times as you want, so probably, your product key for Windows 7 and Windows 8.1 can be used for re-activating Windows 10 automatically in case that happens.
“You will not need your 8.1 key, the same device will reactivate once it has been successfully upgraded to 10,” Aul has explained.
Windows 10 will be supported on PCs and laptops eligible for the free upgrade for the entire life of the device, so once the one-year free upgrade window comes to an end, you will continue to receive updates and security patches.