I haven't experiences this with gpt-5.3-codex (xhigh) for example. Opus/Sonnet usually work well when just released, then they degrade quite regularly. I know the prompts are not the same every day or even across the day, but if the type of problems are always the same (at least in my case) and a model starts doing stupid things, then it means something is wrong. Everyone I know who uses Claude regularly, usually have the same esperience whenever I notice they degrade.