Abstract We test the localization model (LM) prediction of a parameter-free relationship between the α-structural relaxation time τ _α and the Debye–Waller factor 〈u ² 〉 for a series of simulated glass-forming Cu–Zr metallic liquids having a range of alloy compositions. After validating this relationship between the picosecond (‘fast’) and long-time relaxation dynamics over the full range of temperatures and alloy compositions investigated in our simulations, we show that it is also possible to estimate the self-diffusion coefficients of the individual atomic species (D _Cu, D _Zr) and the average diffusion coefficient D using the LM, in conjunction with the empirical fractional Stokes–Einstein (FSE) relation linking these diffusion coefficients to τ _α . We further observe that the fragility and extent of decoupling between D and τ _α strongly correlate with 〈u ² 〉 at the onset temperature of glass-formation T _A where particle caging and the breakdown of Arrhenius relaxation first emerge.