Coskrew: Hi everyone, are all the games compatibles with Windows 8.1?
Thank you.
ChrisSD: I use Windows 8.1 and haven't had any trouble. You may want to check the game's page to make sure but I think all the games that support 7 now support 8 and 8.1?
Nope, each version of Windows is listed individually and those are the only ones GOG has officially tested and blessed as working. If a game doesn't list a particular Windows release it is either because it didn't pass GOG's testing adequately enough to get the blessing, or it didn't work at all, or it hasn't been tested yet. One may or may not get a game to work that does not list their operating system version as being officially supported though and it will definitely vary from game to game, might depend on what video hardware you have or what version of the drivers and other factors.
It is a bad idea though to assume "Windows 7 support" automatically means anything else other than "tested and seems to work reliably on Windows 7 so we support that officially". GOG does try to help get games working on any Windows release if possible though or at least point people to things to try in the forums etc. Just be cautious though to avoid headaches.