I’ve seen a couple solo efforts and a couple teams, but usually a few months. It tends to evolve as a kind of whack-a-mole situation - “we solved that failure case/hallucination, now we’re getting this one.”
My sense is that these are organizations where they probably recreated, with some minor details changed, the same problems they already had. Under planned and over-engineered in the attempt to fix and if things ever work it's more from some awful meta stable chaos than anything else.