Since the Maastricht Treaty, differentiated integration has been regulated in EU primary law. Despite the increase of differentiation tools through Treaty revisions, instances of “atypical” differentiation, i.e. differentiated integration beyond the primary law framework, have emerged in recent practice. On the one hand, most cases of differentiation through partial agreements can be categorized as atypical. On the other, atypical differentiation has also been achieved through secondary EU law, the most prominent case being the banking union. Focusing on the latter type of atypical differentiation, the paper sheds light on what this trend may add to our understanding of differentiated integration. First, atypical differentiation may call into question scholarly efforts to categorize the phenomenon of differentiation. Secondly, and more importantly, if this practice were to be generalized, would enhanced cooperation, with its substantive and procedural constraints, still be needed?