A growing body of research devotes attention to new venture evolution in uncertain and ambiguous environments. Extant literature recognizes the importance of adaptation as a key aspect of this evolution but lacks a detailed understanding of the micro-processes through which new ventures can evolve into an optimal archetype. Building on an ethnographic study of a new venture, we introduce “archetype legitimacy” as an important contingency to distinguish between experimental and structural processes of archetype adaptation. Before legitimacy is obtained, experimental adaptation prevails and is realized through mechanisms of resource relaxation and business model learning. After legitimacy, structural adaptation takes place, which is realized through prospective processes of sense-giving to the new business model, sense-breaking of the old business model and resource ambidexterity.