Parton distribution functions (DFs) are a preeminent source of hadron structure information; and experiments interpretable in terms of hadron DFs have long been a priority. For much of this time, DFs were inferred from global fits to data and viewed as benchmarks. Such fitting remains crucial, providing input for the conduct of numerous experiments worldwide. But the past decade has seen the dawn of a new theory era, with continuum and lattice studies of quantum chromodynamics beginning to yield robust DF predictions. This presentation will describe the first unified set of predictions for proton and pion DFs -- valence + glue + four-flavour-separated sea, and explain what their similarities and differences reveal about emergent hadron mass.