How to determine whether mobile Union citizens have a right to social assistance? Research has shown how Western European Member States have made efforts to restrict Union citizens' access to their welfare systems over the past decade, whereby lawful residence has increasingly become the linchpin for entitlement. Member States have responded strikingly differently, however, to the complex administrative puzzle of dealing with open borders, the ability to verify lawful residence and the right to social assistance over time. This article makes an analytical and empirical contribution to existing literature by asking how Member States adjust their welfare/migration administrations to fit the Union's free movement regime and what implications this has for Union citizens. Based upon comparative case studies into the administration of social assistance rights in Germany, Austria and the Netherlands, the article develops a typology of three different models of administering Union citizens' access to the welfare state: the form, signal and delegation models. Demonstrating how bureaucratic design impacts the stratification of social rights in the Member States in different ways, the article concludes that studying alternative administrative models offers important insights into the functioning of territorial welfare states in open border regimes.