Under EU law, EU citizens constitute a particular group of immigrants, as they can, mostly without restrictions, move to, and reside in, another EU country, enjoying equal treatment with nationals in terms of accessing employment and social rights. However, as this article demonstrates, the settlement of EU citizens in another member state does not happen without hurdles. Through a careful in‐depth study of access to transnational welfare rights in practice, we analyse knowledge and resulting power asymmetries impacting interactions between certain EU migrant claimants and street‐level bureaucrats in Austrian and German social administrations. Following an inductive approach, based on an extensive data set of 144 qualitative interviews, this article first unpacks the different types of knowledge asymmetries relating to administrative procedures, formal social entitlements and the German language. We then analyse how such knowledge asymmetries may open space for welfare mediation in order to compensate for a lack of German language skills and to clarify misunderstandings about legal entitlements and obligations embedded in the claims system. Finally, our contribution offers a typology of welfare mediators and their characteristics, as not all types can be regarded as equally effective in reshaping power asymmetries. Overall, this article allows for insights into how welfare mediators, as more or less institutionalised opportunity structures, can shift policy outcomes in unexpected ways, enabling access to social benefits and services for otherwise excluded EU migrant citizens working, or seeking to work, in another EU member state.