Model drift

The model behind an API endpoint is not a fixed artifact: providers retrain, swap checkpoints and adjust system prompts, and behavior changes without a version bump. A prompt that worked in March can silently degrade by June — the linked findings include measured drift on identical prompts across months. For anything in production this turns testing from a release activity into a monitoring activity: pin versions where you can, and re-run your evals on a schedule where you can't.