Offline evals are a proxy for production, and the proxy degrades as the input population shifts. Online monitoring samples live traffic, scores it against expectations (automatically or with an LLM judge), and tracks distribution drift. A standardized drift score turns 'it feels worse' into an alert.
Sample and score
Continuously sample production requests and score a subset to estimate live quality.
Distribution drift
Track the mean and spread of inputs and scores. A shift in either signals that the offline eval no longer represents traffic.
Bound the blast radius
Canary deploys expose a small fraction of traffic first, so drift and failures surface before full release.