I used to think that when Threads talked about joining the Fediverse, it was just talk. Now it seems they are serious. However, there are currently two issues. First, when you view a Threads.net user on Mastodon, you can only see their posts but not their followers and following. I guess Threads wants to keep their valuable social graph (largely migrated from Instagram) within their own platform. The other issue is that you can't find Mastodon users on Threads, so this interoperability is only one-way. In conclusion, Threads has finally taken this step to attempt to join the Fediverse, but it still has some way to go before achieving true open interoperability. However, it is worth looking forward to.