Drift happens silently. No error is thrown. The model appears functional while outputs become increasingly wrong. Types include data drift (input distribution changes), concept drift (the relationship between inputs and correct outputs changes), and model drift (degradation from both).

Drift is how trusted agents become untrustworthy without anyone noticing. Detecting drift requires continuous measurement, not periodic review. A steadily worsening BTS trend is the earliest detectable signal.

BTS trends across telemetry batches serve as the drift signal. A steadily declining behavioral consistency or rising anomaly rate score is the earliest detectable symptom. The license_score_history table enables trend analysis invisible in point-in-time audits.