Now with the free Windows 10 upgrade offer no longer available, Microsoft changed its mind and says it will support the Skylake platform to the end-of-life (EOL) dates of the applicable operating system:
In the case of Windows 7, that's 14 January 2020, and for Windows 8.1 it's 10 January 2023. For users of Windows 8, that product is actually already EOL and you should update to Windows 8.1 immediately - though Windows 10 is no longer available as a freebie, the 8 to 8.1 path remains open and indeed highly recommended.
Microsoft explains: "This change is made possible through the strong partnership with our OEM partners and Intel who will be performing security update validation testing and upgrade testing for 6th Gen Intel Core systems running Windows 7 and Windows 8.1 through the end of support dates."