What do you mean by 'fully'? I mean, with a lot of hard work, sweat, and cursing that comes with making any large game, not to mention a game engine and various support infrastructure too, there's at least one existence proof that they're at least 'working': https://kandria.com/ (How much cursing has been done at Windows vs SBCL vs OpenGL vs various libraries, only Shinmera knows. You might like a recent overview he wrote up of some of the development: https://reader.tymoon.eu/article/413 When things work well enough that "build with wine" is a viable strategy, that's pretty well in my book.)
A quick scan of the git page revealed references to Windows 2000, NT and XP (SP3 even!) but I didn't see mention of even Vista, nor anything newer.
A slightly longer look revealed an email from 2013 which seemed to speculate about the level of effort required to move to 64 bit support. So .. probably the short answer here is 'no'.
