Threads has begun testing federation over ActivityPub. And they have blocked two important servers I administrate. The first server is the Mostr Bridge. The Mostr Bridge connects ActivityPub and Nostr together, so people can communicate across protocols. The second server is Spinster.xyz, which is arguably the largest independent feminist community online.
Still the nostr bridge has never caused any problems
I’m not super familiar with them but mastodon.social is currently limiting them for spam.