According to Microsoft, the company stopped selling Windows 7 Professional or any version of Windows 8.1 to OEMs as of 31 October 2016.
Now only Windows 10 has been left as a long term choice for OEMs.
Organizations with enterprise licensing agreements and Software Assurance may continue to purchase new PCs, then downgrade the OS from the already installed Windows 10 to Windows 7 if they want to keep using the older edition.
OEMs will still be allowed to sell new computers with Windows 7 until their supply of licenses dries up. Then its only Windows 10.
Support for Windows 7 will continue until 14 January 2020 and windows 8.1 until 10 January 2023. This gives users another 3 years to plan their migration.