ABSTRACT
Informal rules are an underexplored component of collaborative governance, yet they play a critical role in digital transformation projects. This study examines their functions and constraints through a longitudinal case study of the Hui-Tian City Brain project in Beijing. Drawing on government documents, media reports, and interviews with officials, IT enterprises, and civil servants, we trace the emergence and evolution of the informal ‘product recommendation meeting’ rule. This rule streamlined deliberation by reducing information asymmetries, lowering coordination costs, and facilitating joint action across sectors. However, its effectiveness was constrained by the high transaction costs of repeated face-to-face meetings and the limited, invitation-based caucus structure of collaboration. The findings show that informal rules can both enable and restrict collaboration in digital transformation. We argue for greater attention to informal institutional arrangements in understanding and designing collaborative governance.