The archive.today operator claims on his blog that this was nothing major: https://lj.rossia.org/users/archive_today/

> Regarding the FBI’s request, my understanding is that they were seeking some form of offline action from us — anything from a witness statement (“Yes, this page was saved at such-and-such a time, and no one has accessed or modified it since”) to operational work involving a specific group of users. These users are not necessarily associates of Epstein; among our users who are particularly wary of the FBI, there are also less frequently mentioned groups, such as environmental activists or right-to-repair advocates.

> Since no one was physically present in the United States at that time, however, the matter did not progress further.

> You already know who turned this request into a full-blown panic about “the FBI accusing the archive and preparing to confiscate everything.”

Not sure who he's talking about there.