The problem of glass relaxation is traditionally known as one of the most challenging problems in condensed matter physics, with important implications for several high-tech applications of glass. In this study, we present a predictive model for the temperature, thermal history, and composition dependence of glassy relaxation dynamics. Our model enables, for the first time, the quantitative prediction of relaxation behavior for new glass compositions. Using the commercial Corning EAGLE XG ® alkaline earth aluminosilicate glass as a reference, the model gives accurate predictions of the nonequilibrium viscosity for 4 other aluminosilicate glasses, covering both alkali-free and alkali-containing compositions, without any free fitting parameters. Using the composition-dependent nonequilibrium viscosity model, only the measured values of the glass transition temperature and fragility are required to predict the nonequilibrium viscosity as a function of both temperature and thermal history. The range of glass transition temperatures of the 4 verification glasses covers about 200°C, while that of fragility values is about 6. As such, this work gives insights into the structural origin of nonequilibrium viscosity and can enable the future design of glass compositions with tailored relaxation behavior.