Users are reporting success activating clean installations of Windows 10 using old license keys, and specifically those that apply to Windows 7, Windows 8, and Windows 8.1. This method continues to work even after the Creators Update, which is the second major upgrade to Windows 10 since it was made available to the public in July 2015 (the

Source: Hot Hardware – Windows 10 Creators Update Can Still Be Activated With Old Windows License Keys