Nothing happened. That is the strange part.
No deploy. No pull request. Nobody touched the prompt. Your agent ran the way it always ran on Friday, and it runs on Monday, and every dashboard is green. Then a ticket comes in about an answer nobody on your team would have written, and you go looking for the change that caused it, and there is no change on your side. There was a model upgrade.
It is the only change to your system that you did not make, cannot find in your own git history, and usually cannot roll back on your own schedule. It is also the one most likely to be announced to you as good news.
Why a model upgrade does not look like a bug
Because it is not one. The new model really is better. Better on reasoning, better on code, better on the evaluations the lab published beside it, and probably better on yours too, if what you measured was the average.
