Maybe they're still massing, but there were articles about this at least a week ago.

Signs U.S. Massing B-2 Spirit Bombers In Diego Garcia

B-2 Bombers Arrive on Diego Garcia in Unusual Show of Force

And, the thing about B-2s in Yemen was older, my bad. It was in the sidebar, but was from last year...because we're just constantly bombing the shit out of Yemen:

Questions Linger Over Australia’s Role In B-2 Spirit Strikes On Yemen (Again, last year, not current strikes)