GPT 5.2 codex plans well but fucks off a lot, goes in circles (more than opus 4.5) and really just lacks the breadth of integrated knowledge that makes opus feel so powerful.
Opus is the first model I can trust to just do things, and do them right, at least small things. For larger/more complex things I have to keep either model on extremely short leashes. But the difference is enough that I canceled my GPT Pro sub so I could switch to Claude. Maybe 5.3 will change things, but I also cannot continue to ethically support Sam Altman's business.
I'd say that GPT 5.2 did slightly better on the stuff that I'm working on currently compared to Opus 4.5, but it's rather niche - a fancy Lojban parser in Haskell). However Opus is much easier to steer interactively because you can see what it's doing in more detail (although 5.3 is much improved in that regard!). I wouldn't feel empty-handed with either model, and both wrote large chunks of code for this project.
All that said, the single biggest reason why I use Codex a lot more is because the $200 plan for it is so much more generous. With Claude, I very quickly burn through the quota and then have to wait for several days or else buy more credit. With Codex, running in High reasoning mode as standard with occasional use of XHigh to write specs or debug gnarly issues, and having agents run almost around the clock in the background, I have hit the limit exactly once so far.
Didn't make a difference for me. Though I will say, so far 4.6 is really pissing me off and I might downgrade back to 4.5. It just refuses to listen to what I say, the steering is awful.
Opus is the first model I can trust to just do things, and do them right, at least small things. For larger/more complex things I have to keep either model on extremely short leashes. But the difference is enough that I canceled my GPT Pro sub so I could switch to Claude. Maybe 5.3 will change things, but I also cannot continue to ethically support Sam Altman's business.