Graphene with angstrom‐scale, zero‐dimensional pores offers a promising platform for gas separations due to its exceptional permeance and potential for molecular sieving. Herein, we demonstrate a dynamic strategy to tune N‐functionalized graphene pores, achieving selective oxygen (O 2 ) separation from nitrogen (N 2 ), a particularly challenging separation due to their similar kinetic diameters. We exploit the heterogeneity of functional groups at the pore edge to tune the pore limiting diameter (PLD). By facile thermal annealing, we convert primary amine groups at the pore edge to lattice‐incorporated nitrogen. Temperature‐dependent extent of conversion allows to tune the steric hindrance from amine‐CO 2 complex, and therefore, PLD for O 2 /N 2 separation in favor of O 2 permeation. The resulting membranes exhibit attractive O 2 /N 2 separation performance, with O 2 permeance near 2500 GPU with O 2 /N 2 selectivity above 10, significantly outperforming the state‐of‐the‐art membranes. This is attractive for energy‐efficient and modular production of O 2 from air and can cut down fuel consumption in natural gas‐fired furnaces in the chemical industry by 60%.