I've found GPT-5-Codex (the model used by default by OpenAI Codex CLI) to be superior but, as others have stated, slower.
Caveat, requires a linux environment, OSX, or WSL.
In general, I find that it will write smarter code, perform smarter refactors, and introduce less chaos into my codebase.
I'm not talking about toy codebases. I use agents on large codebases with dozens of interconnected tools and projects. Claude can be a bit of a nightmare there because it's quite myopic. People rave about it, but I think that's because they're effectively vibe-coding vastly smaller, tight-scoped things like tools and small websites.
On a larger project, you need a model to take the care to see what existing patterns you're using in your code, whether something's already been done, etc. Claude tends to be very fast but generate redundant code or comical code (let's try this function 7 different ways so that one of those ways will pass). This is junior coder bullshit. GPT-5-Codex isn't perfect but there's far far less of that. It takes maybe 5x longer but generates something that I have more confidence in.
I also see Codex using tools more in smart ways. If it's refactoring, it'll often use tools to copy code rather than re-writing the code. Re-writing code is how so many bugs have been introduced by LLMs.
I've not played with Sonnet 4.5 yet so it may have improved things!
Codex-cli doesn't require Linux or WSL. I've been using it on Windows all week. That said, the model seems to get confused by Powershell from time to time, but who doesn't?
You should really try it in WSL or proper Linux, the experience is vastly different. I've mostly been using Codex (non-interactively though) for a long time on Linux. I tried it out on Windows just the other day for the first time and quoting + PowerShell seems to really confuse it. It was borderline unusable for me as it spent most of the reasoning figuring out the right syntax of the tooling, on Linux there is barely anything of that.
You're right. Tried it out this morning, and it uses fewer tokens and gets the job done quicker, not wasting so much time on the Powershell nonsense. I was resisting setting up WSL because this is just a temporary workstation, but it was worth it