GPT-5.3-Codex review after 4 days of use

I ‘ve been testing GPT-5.3-codex on UI code and a long running task: refactor a large typescript backend API, in particular doing authz, sql optimizations, and other vulnerability checks. It ran for 4 days with some interruptions.

The Good:

- fast, its thorough, it works well

- great for UI as the quick speed gives you a fast feedback loop

- writes way better code than previous models

The Bad:

- too eager to take action (seems the system prompt biases action), superficial and doesn’t seem to go as deep as gpt-5.2-high does unless your prompts are on point

- prone to pigeon holeing into repetitive behavior not essential to my original ask despite very explicit and careful prompts (it outright ignores or forgets)

- with UI at times it can get very stubborn and not react or listen to any new info or instructions and will require several prompts to get it to “wake up”

https://promptcoding.substack.com/p/gpt-53-codex-review-after-2-days