An efficient multiscale constitutive framework for nickel-base superalloys is proposed that enables the incorporation of strain gradient effects. Special interface regions in the unit cell contain the plastic strain gradients that govern the development of internal stresses. The model is shown to accurately simulate the experimentally observed size effects in the commercial alloy CMSX-4. The limited complexity of the proposed unit cell and the micromechanical simplifications make the framework particularly efficient in a multiscale approach. This is demonstrated by applying the model in a gas turbine blade finite element analysis.