Ontological drift is the failure the model cannot catch by measurement, because it is a failure of what the measurements are for. It names the gap between what a form claims to be and what it has actually become — and its most dangerous version is not decline but the opposite: a form becoming more efficient than ever at exactly the moment it becomes obsolete.
At every scale
It happens to a person — someone with money, status, family, and health struck by an emptiness that measurement cannot see (accurately called a loss of purpose, and also asking whether the existing form is failing to carry what matters). It happens to a civilization — a society better than ever at producing goods once production is no longer the central problem, at educating workers once workers are less necessary, at capturing attention while attention-capture hollows out interior life. Efficiency is no defense against drift; it is often the disguise. The signal that drift is underway is frequently not a metric at all but unease, refusal, grief, absurdity, or this cannot be all there is — which is why the model treats such signals as data rather than noise. Because every living form eventually drifts, the model treats drift not as failure but as a first principle to design for — the everyday machinery for that is designing for drift. See What Is It All For?.