It's hard to compare the two tools because they change so much and so fast.

Right now, as an example, claude code with opus 4.5 is a beast, but before that, with sonnet 4.0, codex was much better.

Gemini-cli, on the other hand, with gemini-flash-3.0 (which is strangely good for the "small and fast" model), it's very good (but the cli and the user experience are not on par with codex or claude yet).

So we need to be in constant observations of those tools. Currently (after gemini-flash-3.0 came out), I tend to submit the same task to claude (with opus) and gemini to understand the behaviour. gemini is surprising me.