Windows customers have two options right now when it comes to upgrading previous versions of the operating system to Windows 10.
They can either upgrade a Windows 7 or 8 system directly to Windows 10 for free, or use Microsoft's offer for customers who use assistive technologies to upgrade to Windows 10 for free.
The first option is unofficial, but it still works more than a year after Microsoft stopped the "get Windows 10" offer for good.
The second option is official, but it is only available for customers who use assistive technologies. Note that Microsoft does not enforce the requirement.
If you open the Windows 10 Upgrade page for customers who use assistive technologies right now, you may notice that Microsoft changed some parts of it recently.
Microsoft did not reveal an end date for the offer back when the company introduced it. This changed with the recent update of the content of the page, as the end date is now listed as December 31, 2017.
If you use assistive technologies, you can upgrade to Windows 10 at no cost as Microsoft continues our efforts to improve the Windows 10 experience for people who use these technologies. Please take advantage of this offer before it expires on December 31, 2017.
Microsoft highlights the end date in the first paragraph on the upgrade to Windows 10 page, and reveals it also in the FAQ section on the same page.
This means that customers who use assistive technologies can use the offer to upgrade to Windows 10 for free only this year. The offer expires on the last day of the year, and won't be available anymore.
The loophole free upgrade to Windows 10 may still work though, and that is then still an option for users who want to upgrade machines running Windows 7 or 8.1 to Windows 10.
Windows users who are not sure if Windows 10 is right for them can take advantage of the offer, and roll back their systems afterwards. The license is linked to the Microsoft Account if you use it, or the hardware ID, so that you have it in case you want to upgrade to Windows 10 in the future. (via Deskmodder)