Copyright Office's interpretation of US copyright laws says that AI is not human, thus not an attributable author for copyright registration, and output based on mere prompting is no one's IP, it can't be copyrighted[1].

When AI output can be copyrighted is when copyrighted elements are expressed in it, like if you put copyrighted content in a prompt and it is expressed in the output, or the output is transformed substantially with human creativity in arrangement, form, composition, etc.

[1] https://newsroom.loc.gov/news/copyright-office-releases-part...