@profcarroll We're all reading tea leaves. My take is that in an early stage posts from Threads will federate OUT, but posts from the Mastodon/etc Fediverse will not federate IN to Threads -- for that early phase. (Which makes sense from a dev POV)
Crawl, walk run.
So replies back to Threads posts from the Fedi, and DM's to Threads users from the Fedi would not be seen by Threads users initially.