A grand challenge for proton exchange membrane electrolyzers is the rational design of oxygen evolution reaction electrocatalysts to balance activity and stability. Here, we report a support-stabilized catalyst, the activated ~200 nm-depth IrW nanochannel that achieves the current density of 2 A cm-2 at an overpotential of only ~497 mV and maintains ultrastable gas evolution at 100 mA cm-2 at least 800 h with a negligible degradation rate of ~4 μV h-1. Structure analyses combined with theoretical calculations indicate that the IrW support alters the charge distribution of surface (IrO2)n clusters and effectively confines the cluster size within 4 (n≤4). Such support-stabilizing effect prevents the surface Ir from agglomeration and retains a thin layer of electrocatalytically active IrO2 clusters on surface, realizing a win-win strategy for ultrahigh OER activity and stability. This work would open up an opportunity for engineering suitable catalysts for robust proton exchange membrane-based electrolyzers.