Hydrogen (H) is essential to decarbonize industry, but its use today is limited because it embrittles the metals and alloys required to store/distribute it. Despite 150 years of research, the fundamental mechanisms of H-embrittlement are still poorly understood. H atoms form a solid solution of interstitials in structural metals that affect the behavior of dislocations. While dislocations are essential to understand plasticity and deformations, it is still unclear whether H enhances or reduces their mobility. This matter is hotly debated, as no technique can measure dislocations and their motion deep inside bulk crystals during stress. We developed time-resolved and 3D dark-field X-ray microscopy (DFXM) and use it to study the interactions of deep subsurface dislocations. We now seek to use DFXM to directly measure how H alters the structure and interactions forces between dislocations, offering the first direct measurements to reconcile conflicting H-altered mobility models.