We’ll have to wait and see how good their neural hashing is, but just to clarify the 1 trillion number is the “probability of incorrectly flagging a given account” according to Apple’s white paper.
I think some people think that’s the probability of a picture being incorrectly flagged, which would be more concerning given the 1.5 trillion images created in the US.
Source: https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...