Abstract: Hydrogen partitioning between liquid iron alloys and silicate melts governs its distribution and cycling in Earth’s deep interior. Existing models based on simplified Fe-H systems predict strong hydrogen sequestration into the core. However, these models do not account for the modulating effects of major light elements such as oxygen and silicon in the core during Earth’s primordial differentiation. In this study, we use first-principles molecular dynamics simulations, augmented by machine learning techniques, to quantify hydrogen chemical potentials in quaternary Fe-O-Si-H systems under early core–mantle boundary conditions (135 GPa, 5000 K). Our results demonstrate that the presence of 5.2 wt% oxygen and 4.8 wt% silicon reduces the siderophile affinity of hydrogen by 35%, decreasing its alloy–silicate partition coefficient from 18.2 (in the case of Fe-H) to 11.8 (in the case of Fe-O-Si-H). These findings suggest that previous estimates of the core hydrogen content derived from binary system models require downward revision. Our study underscores the critical role of multicomponent interactions in core formation models and provides first-principles-derived constraints to reconcile Earth’s present-day hydrogen reservoirs with its accretionary history.