Flexible social inference facilitates targeted social learning when rewards are not observable

Relying on others can be as risky as it can be rewarding. Advice seekers must disentangle good advice from bad, and balance the potential benefits of shared wisdom against the risks of being misled. Groups are most effective at sharing information and solving problems together when everyone is sensitive to ``who knows what.'' Acquiring such knowledge in the first place, however, is not trivial -- especially in contexts where background information is limited. What underlying cognitive abilities are needed for social learning to be useful in information-limited environments? Here, we propose that the capacity for flexible social inference plays a key role in human group behavior, allowing latent properties such as success or skill to be inferred from others' outward behavior even when there is no direct access to others' private rewards and "success" manifests differently from context to context. We begin by formalizing our proposal in a cognitive model and comparing this model's predictions against those of simpler heuristics in a series of computational simulations. We then evaluated these predictions in three large-scale behavioral experiments using a multi-agent search paradigm with hidden rewards. In Experiment 1, we found that average performance improves as a function of group size at a rate predicted by our model but not by three simpler alternatives. In Experiment 2, we placed human participants in controlled scenarios with artificial agents to more systematically evaluate the conditions under which people choose to rely on social information. Finally, in Experiment 3, we generalized these findings to a more complex and noisy environment, suggesting regimes where inferences may break down. Taken together, we find that even the most rudimentary social cognition abilities may facilitate the characteristic flexibility of human collective behavior.