Abstract The moment‐duration (M0‐T) scaling law reveals fundamental earthquake physics across various sizes and tectonic settings. However, the validity of the cubic relation (M0 ∝ T3) inferred for large (Mw ≥ 7) megathrust events has been recently questioned due to the scarcity of observations and similarities to slow earthquakes. Here, by compiling events over the past 500 years from global subduction zones, we double the number of earthquakes studied (>260) compared to previous studies. A possible scale change is observed, at moment‐magnitude and duration of ∼7.6 and ∼38.1 s, respectively. The new catalog reveals an accelerated decrease of the scaling exponent as a function of magnitude from 2.5 (Mw ≥ 7) to below 1 (Mw > 8.7), indicating increasingly longer durations than expected for larger events. The rapid increase in duration with earthquake size is interpreted as the interplay of seismogenic bounds, trench‐breaching, and subevents, which delays lateral rupture propagation. Our study aids in understanding slow and fast earthquakes.