They previously announced that they would federate with ActivityPub, but yesterday we learned that it won't happen for "three months." With all the European regulatory issues and other factors, I'll bet it will be a lot longer than that. In fact, I'd be surprised if we ever see full federation capability.
They haven't said why. I'm assuming that federation with outside entities would present some logistical problems for them w/r/t their privacy obligations in Europe. If that's right, I suspect the whole ActivityPub thing could be "delayed" indefinitely.