ABSTRACT Manganese‐based layered oxides are among the most promising cathode materials for potassium‐ion batteries. Yet their application is hindered by issues like poor structural stability and multiple phase transitions. Herein, the occupancy ratio (K t /K h ) of the conventional triangular prism center site (K t ) to the previously unknown KO 14 hexagonal prism center site (K h ) is finely tuned to stabilize the layered oxide framework for P3‐type K x MnO 2 cathodes. The first‐principles calculations along with ex‐situ X‐ray diffraction, aberration‐corrected scanning transmission electron microscopy, and K L‐edge soft X‐ray absorption spectroscopy reveal that the K + at the K h site are locally pinned as self‐pillars, where moderate K h pillars stabilize the oxide framework by suppressing phase transitions and facilitating a solid‐solution K + storage mechanism, while excessive K h immobilizes ions and blocks diffusion pathways. The K content and thermal treatment are functionally interconnected and determine the K h fraction and phase evolution. The K 0.5 MnO 2 cathode with an optimal (K t /K h ) ratio delivers excellent high‐rate performance of 46.1 mAh g −1 at 2 A g −1 and maintains 76.7% of its initial capacity after 2000 cycles at 1 A g −1 . This work demonstrates the potential benefits of alkali‐ion occupancy engineering as a versatile strategy for stable layered oxide cathodes in high‐performance alkali‐ion batteries.