That's right, that's really "git gc". It's the first version of it in JGit. Not all the semantics of git gc are there. But currently it does a pack-refs, repack and prune. Specifically for prune JGit also has learned to understand config param gc.pruneExpire. Since it is the first version of GC in JGit and since it is a potentially dangerous operation we are not advertizing it heavily to EGit users. We want to get more experiences with it before we put it to a more prominent place or support automatic garbage collection.
And yes, there are also missing features: we don't do reflog_expire and rerere_gc currently. We are also not moving objects from packfiles to the object directory when they get unreferenced. But the basic functionality is working.