Microsoft has confirmed that OEMs will no longer be allowed to sell new computers with Windows 7 or 8.x after October 31, 2016. If you buy a new PC after that date, you won’t have any options besides Windows 10.
Support for Windows 7 – including security updates – will continue to 2020, so it’s still a perfectly viable operating system. But it’s unclear whether you will still be able to purchase Windows 7 OEM separately, from Microsoft or any other seller, after October 31, 2016. I certainly hope so, although it seems unlikely. So if you’re planning to build any new Windows 7 computers between October 2016 and 2020, you should stock up on Windows 7 OEM licenses now.