We haven't implemented federation of Groups yet, but group tags and discussion
on how unbounded groups can be federated via ActivityPub has already started.
Concerning federation of traditional groups, we will port our logic from v2 and
translate following the same rules as AndStatus because they work, as yvolk beautifully stated :)
Finally, also note that the group actors now have "self-tags", as the other actors, which was a milestone.