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 first one was the Anniversary Update). Microsoft made it known that Windows 7 and Windows 8/8.1 users would have a full year to upgrade their PCs to Windows 10 at no cost. Technically that offer expired around nine months ago. Be that as it may, users have been finding ways to install Windows 10 for free or at a lower cost than purchasing a brand new license.

One of those ways is by taking advantage of Microsoft's grace period for anyone who uses assistive technologies. Microsoft continues to offer free upgrades in such cases, and since this is based on the honor system—Microsoft does not take any steps to verify that a user qualifies—it is up to each user's own moral compass whether to go this route or not.

With Microsoft still allowing Windows 10 to activate with old Windows keys, users may find it less expensive to purchase a Windows 7 or Windows 8/8.1 license online. We did a quick web search and were able to find a Windows 7 Pro OEM key for less than $10. Whether using an old key is completely legal or not is up for debate. There is also the risk of Microsoft could update its servers to block Windows 10 activation with old Windows keys. We'd be surprised if it did, as Microsoft seems much more interested in getting as many people on Windows 10 as possible. It has a longer term game plan in mind, with a stated goal of having 1 billion active Windows 10 devices in the next 15 months. At present, there are 400 million active Windows 10 devices, according to Microsoft's latest official update.