It's really not that hard. Codex = The model trained specifically for programming tasks. You want this if you're writing code. GPT5.2 = The current version. Y

It's really not that hard. Codex = The model trained specifically for programming tasks. You want this if you're writing code. GPT5.2 = The current version. You don't have to think about this, you just use the latest. High Reasoning = A setting you select for balancing between longer thinking time or quicker answers. It's usually set and forget.