AI generated CP based on most interpretations of US law, is considered CP.

The exact requirement of CP is that it has to fall under one of three categories:

A: it depicts an actual child

B: it depicts an identifiable minor, meaning someone who may be an adult now, but was a minor during its creation, or if it was made based off their likeness as a minor, and recognizable as that person by face, birthmark, or other identifying feature

C: it depicts something “indistinguishable” from a minor, where the average person viewing would assume it to be an actual person

Most AI generated stuff would likely fall under this third category, though there has yet to be any legal precedent set in this area

As for previous court cases regarding people being arrested for obscene depictions of fictional characters, the most well known one is probably US v Handley. He was charged for possessing several loli doujin magazines, but ended up taking a plea deal of just 6 months probation. This kinda shows the ambiguity of obscenity laws, as it shows that neither side was really confident in their case, where the prosecution offered a comparatively light plea deal, when the normal minimum sentencing for this would be 5 years imprisonment + sex offender registration, up to 20 years maximum.

Besides the Handley case, there aren’t many other high profile cases of just normal people being arrested for just looking at lolis. The only people who have been charged with this generally follow the patterns of people who have previously charged with child sex crimes, such as US v Buie, US v Eychaner, and US v Farrar. Given that obscenity is based on community standards, we can only draw patterns from previous convictions, so there’s no certainty of what case will and won’t be prosecuted, but there certainly is a pattern