The structure of glassy GeSe9 was investigated by combining neutron diffraction with density-functional theory-based ﬁrst-principles molecular dynamics. In the simulations, three different models of N = 260 atoms were prepared by sampling three independent temporal trajectories, and the glass structures were found to be substantially different from those obtained for models in which smaller numbers of atoms or more rapid quench rates were employed. In particular, the overall network structure is based on Se_n chains that are cross-linked by Ge(Se4)1/2 tetrahedra, where the latter are predominantly corner as opposed to edge sharing. The occurrence of a substantial proportion of Ge-Se-Se connections does not support a model in which the material is phase separated into Se-rich and GeSe2-rich domains. The appearance of a ﬁrst-sharp diffraction peak in the Bhatia Thornton concentration-concentration partial structure factor does,however,indicate a non-uniform distribution of the Ge-centered structural motifs on an intermediate length scale.