Solid state potassium (K) metal batteries are intriguing in grid‐scale energy storage, benefiting from the low cost, safety, and high energy density. However, their practical applications are impeded by poor K/solid electrolyte (SE) interfacial contact and limited capacity caused by the low K self‐diffusion coefficient, dendrite growth, and intrinsically low melting point/soft features of metallic K. Herein, a fused‐modeling strategy using potassiophilic carbon allotropes molted with K is demonstrated that can enhance the electrochemical performance/stability of the system via promoting K diffusion kinetics (2.37 × 10−8 cm2 s−1), creating a low interfacial resistance (≈1.3 Ω cm2), suppressing dendrite growth, and maintaining mechanical/thermal stability at 200 °C. A homogeneous/stable K stripping/plating is consequently implemented with a high current density of 2.8 mA cm−2 (at 25 °C) and a record‐high areal capacity of 11.86 mAh cm−2 (at 0.2 mA cm−2). The enhanced K diffusion kinetics contribute to sustaining intimate interfacial contact, stabilizing the stripping/plating at high current densities. Full cells coupling ultrathin K–C composite anodes (≈50 µm) with Prussian blue cathodes and β/β″‐Al2O3 SEs deliver a high energy density of 389 Wh kg−1 with a retention of 94.4% after 150 cycles and fantastic performances at −20 to 120 °C. An ultrathin K–10% reduced graphene oxide anode is constructed, delivering promoted K diffusion kinetics and mechanical/thermal stability at 200 °C, which creates an interfacial resistance (≈1.3 Ω cm2) with a current density of 2.8 mA cm−2 at 25 °C and an areal capacity of 11.86 mAh cm−2, enabling solid state potassium metal batteries operating at −20 to 120 °C.