The copyright office still holds that human authorship is a core tenet of copyrightability, however, whether or not a submission meets the "de minimis" amount of AI-generated material to uphold a copyright claim is still being decided and refined by the courts and at the moment the distinction appears to fall on whether the AI was used "as a tool" or as "an author itself", with the former covered in certain cases and the latter not.
The registration process makes it clear that failure to disclose submissions in large contribution authored by contractor or ai can result in a rejection of copyright claim now or retroactive on discovery.