The role of materials’ interfaces/grain boundaries on enhancing anion conductivity is an intensely debated issue that has exposed limited understanding on point-defect energetics at interfaces. Using static atomistic simulations on ZrO2 | CeO2 and ThO2 | CeO2 interfaces, we disentangle key interface issues, i.e., oxygen vacancy migration barriers at interfaces in the absence and presence of dopants, and oxygen vacancy-dopant binding energies at interfaces. The results show that, while pure, strained interfaces indeed possess very low oxygen migration barriers, the segregated dopants counteract and significantly raise the barriers. In addition, the dopants bind oxygen vacancies much more strongly at the interfaces than in the bulk, thereby further lowering oxygen diffusivity at interfaces. From our simulations, we conclude that the concept of strained interfaces to enhance anion conductivity prevails primarily in the absence of segregated dopants, and strategies that prevent dopant segregation need to be considered in the design of anion-conducting interfacial materials.