What is model drift?

Providers swap and retune models continuously and rarely announce it in a way that reaches the people measuring outputs. A retuned model can shift an entire category's answers at once.

Drift is invisible to a within-scan confidence band, because that band only describes variation between runs of the same model at the same moment. This is why the model version that answered is worth recording: it is the only way to check a suspicious jump against a change in the machinery.