https://fedipact.online/ is a list of instances that have pledged to preemptively block Threads. Includes my own instance (lemmy.name) among many others.

If lemmy.world doesn’t block very shortly I will move to a different instance.

They won’t. At least not shortly because Threads doesn’t even support ActivityPub, yet, and they want to wait and see according to a post on Mastodon. 👋