Rebus Sic Stantibus in the Age of Artificial Intelligence

This article investigates how the principle of contractual justice - an unwritten yet fundamental source of private law - continues to operate in an era shaped by artificial intelligence (AI). Although pacta sunt servanda remains the cornerstone of contractual certainty, the doctrine of rebus sic stantibus functions as a corrective when radically changed circumstances would make strict performance inequitable. Recognised across all developed legal orders and recently codified in many, the authors analyse the doctrine in more than twenty European jurisdictions, with attention to convergences and doctrinal divergences. The study then turns to smart-contract technology and AI-driven automation, asking whether code-based execution can accommodate contractual justice or instead amplifies contractual rigidity. The authors conclude that automated decision-making can handle only quantifiable adjustments, whereas genuine fairness still requires case-sensitive judicial discretion grounded in unwritten principles. Even - and especially - in the age of AI, therefore, courts - and the normative resources of good faith, fairness and equity - remain indispensable safeguards of contractual balance.