No instances have defederated, because no issuances have federated. Threads does not use activitypub, and is not a federated platform.
They’ve said they will in the future, but these people also say your privacy is safe and that they are serious about fighting disinformation and climate change.
Threads is not federated. It may never be. Anyone is free to plan preemptive action, but I’d like to squash this misunderstanding so everyone knows: none of your current instances are federated with Meta.