Can we trust purpose? Corporate legal forms and built‐in purpose

The literature on corporate purpose rarely considers how legal structures shape fidelity to purpose over time. Yet, recent developments, such as OpenAI's transformation into a Public Benefit Corporation, highlight the critical role of legal forms in determining whether companies can sustain their purpose credibly and over time. We introduce the concept of built‐in purpose as the set of purposes that a legal form can credibly and durably support through its embedded governance mechanisms. Further, we propose a framework to characterize the built‐in purpose of legal forms along two key functions that governance mechanisms must provide to ensure purpose fidelity: a protective function, which safeguards purpose from changing shareholder expectations or external pressures, and an enforcement function, which ensures that the purpose is effectively integrated into managerial decision‐making. We argue that the concept of built‐in purpose enriches the analysis of alternative legal forms and provides a tool for navigating their growing diversity. The alignment between a company's declared purpose and the built‐in purpose of its legal form also constitutes a driver of integrity, opening new perspectives for choosing governance structures suited to each specific purpose.