It is 2 weeks old, but that's also the latest tagged release on github, so it's not out of date. I'm not seeing how to actually get KBFS on linux today.
How about the "keybase-release" package from AUR?
Considering keybase-release[0] was "Last Updated: 2015-11-03 22:36", community/keybase is a lot more recent, but still from January, so not recent enough.