We study efficient allocations when consumers have heterogeneous smooth ambiguity preferences, face model uncertainty, and consider a common set of identifiable models. Aggregate endowment is ambigu- ous. We characterize economies where the representative consumer is of the smooth ambiguity type and find efficient sharing rules. With heterogeneous ambiguity aversion, sharing rules exhibit systematic de- partures from those in vNM-economies and the representative consumer’s nature departs from the typical single-consumer assumption, making for more compelling asset-pricing predictions. We focus on the case where models are point-identified but show that the insights extend when models are only partially-identified.