not sure if I am actually using 5.1-codex-max or just normal 5.1-codex (is there even 5.1-codex?) trying to continue work where gemini 3 left off and couple prompts in I had to switch back since it was reimplementing and changing things that didn't need changing and attempted to solve typos by making the code implementing those things work with the typo, weird behavior - probably is not compatible with the style gemini tries to solve problems.

Just run the /model command in codex and select the model which you want.