Here's a much more reasonable and informed take on the topic, straight from Mastodon's CEO/founder – https://blog.joinmastodon.org/2023/07/what-to-know-about-thr....
Threads will support ActivityPub. They already have UI elements in place for it in the app (like showing your home server domain on your profile), so there's no reason to believe that isn't their intention. The problem, if any, will be on the other end. Plenty of Mastodon/Fediverse servers have already stated their intention of blocking Meta's access to their networks, so even in the best case the end result will be a fragmented mess.