If anyone has doubts about Threads supporting ActivityPub, listen to Mark Zuckerberg on Decoder. Some of what Mark says is almost IndieWeb-esq at times! I still believe Facebook has done a lot of harm to society, but they are clearly hoping to be more open with Threads and that’s a good thing.
https://www.theverge.com/23889057/mark-zuckerberg-meta-ai-elon-musk-threads-quest-interview-decoder