Which statistical tests would you use to detect drift, and what thresholds should trigger action?

Everyone names PSI and KS; almost nobody knows why the KS p-value betrays you at production scale. The thresholds that are actually industry convention, the response ladder behind them, and the trap answer interviewers bait on purpose.

Updated Sep 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.