The reason their naming scheme is so bad is because their initial attempts at GPT-5 failed in training. It was supposed to be done ~1 year ago. Because they'd promised that GPT-5 would be vastly more intelligent than GPT-4, they couldn't just name any random model "GPT-5", so they suddenly had to start naming things differently. So now there's GPT-4.5, GPT-4.1, the o-series, ...