Supplementary Material EMDB reference: SARS-CoV-2 spike in prefusion state, EMD-11328 EMDB reference: SARS-CoV-2 spike in prefusion state (flexibility analysis, 1-up closed conformation), EMD-11336 EMDB reference: SARS-CoV-2 spike in prefusion state (flexibility analysis, 1-up open conformation), EMD-11337 EMDB reference: SARS-CoV-2 stabilized spike in prefusion state (1-up conformation), EMD-11341 PDB reference: SARS-CoV-2 spike in prefusion state, 6zow PDB reference: SARS-CoV-2 spike in prefusion state (flexibility analysis, 1-up closed conformation), 6zp5 PDB reference: SARS-CoV-2 spike in prefusion state (flexibility analysis, 1-up open conformation), 6zp7 Supplementary Figures and Tables. DOI: 10.1107/S2052252520012725/fq5016sup1.pdf Click here for additional data file. Supplementary Movie S1. Movie presenting the morphing between the two algorithmically stable classes described in the main text, spanning principal component axis 1. DOI: 10.1107/S2052252520012725/fq5016sup2.mp4