How can cooperation be sustained in socially heterogeneous settings when institutions explicitly emphasize inclusion and diversity? We study this question in four European cities. Participants face a repeated cooperation dilemma framed as an investment in a local urban amenity. We randomly vary whether the project is described as benefiting the general population or explicitly benefiting a locally relevant marginalized group. We find that inclusive framing has no effect on average contribution levels or beliefs about others’ behavior, however, we document substantial heterogeneity. Minority participants and women increase their contributions under inclusive framing, particularly in later stages of the game. Using the strategy method, we classify individuals into cooperative strategy profiles and show that inclusive framing primarily activates equality-oriented behavioural strategies. Analysis of strategy stability further indicates that inclusion reshapes behaviour within existing strategy profiles rather than inducing shifts across them. Overall, our results suggest that inclusive institutional design can preserve collective action while redistributing cooperative effort across identities and behavioural motivations.