Agreed. My experience is GPT5 is significantly better at large-scale planning & architecture (at least for the kind of stuff I care about which is strongly typed functional systems), and then Sonnet is much better at executing the plan. GPT5 is also better at code reviews and finding subtle mistakes if you prompt it well enough, but not totally reliable. Claude Code fills its context window and re-compacts often enough that I have to plan around it, so I'm surprised it's larger than GPT's.