Achieving stable surface structures of metal catalysts is an extreme challenge for obtaining long-term durability and meeting industrial application requirements. We report a new class of metal catalyst, Pt-rich PtCu heteroatom subnanoclusters epitaxially grown on an octahedral PtCu alloy/Pt skin matrix (PtCu_1.60), for the oxygen reduction reaction (ORR) in an acid electrolyte. The PtCu_1.60/C exhibits an 8.9-fold enhanced mass activity (1.42 A·mg_Pt⁻¹) over that of commercial Pt/C (0.16 A·mg_Pt⁻¹). The PtCu_1.60/C exhibits 140,000 cycles durability without activity decline and surface PtCu cluster stability owing to unique structure derived from the matrix and epitaxial growth pattern, which effectively prevents the agglomeration of clusters and loss of near-surface active sites. Structure characterization and theoretical calculations confirm that Pt-rich PtCu clusters favor ORR activity and thermodynamic stability. In room-temperature polymer electrolyte membrane fuel cells, the PtCu_1.60/C shows enhanced performance and delivers a power density of 154.1/318.8 mW·cm⁻² and 100 h/50 h durability without current density decay in an air/O₂ feedstock.