Professionally, even if GP was to break NDA, it would still take an essay to even begin to describe where they are in order to describe what they're working on, in order to say this thing I'm building, it's being built faster with the help of AI. So the two things are one, hobby projects. Those are greenfield, starting from 0 lines of code. AI is good at that, everyone should try it! The unknown unproven question, thus, is limited to "I have this decades old codebase, can AI actually help?" I am not here to answer that question right now, merely to pose the more specific question you're implying.

I mean, Claude itself has been built by people using Claude. Is that not enough of an example?