<p>All-solid-state lithium metal (Li°) batteries (ASSLMBs) are a promising next-generation energy storage technology due to their use of non-flammable solid electrolytes for enhanced safety and the potential for higher energy density. However, void formation and evolution at the interface between anode and solid electrolyte remains a major challenge, leading to accelerated performance degradation. Departing from traditional interfacial design strategies, here we introduce dynamically adaptive interphases, formed by controllable migration of pre-installed anions in solid electrolytes, to operate ASSLMBs stably under low external pressure. The interphases adapt to the Li° anode volume changes, maintaining close physical contact between the Li° anode and ‘rigid’ solid electrolyte under low or zero external pressure. The dynamically adaptive interphase enables Li° full cells to deliver excellent rate performance and 90.7% of capacity retention after 2,400 cycles at a current density of 1.25 mA cm⁻². Notably, pouch cells with zero external pressure are assembled with 74.4% of capacity retention after 300 cycles. The present work resolves the critical issue of the continuous solid–solid contact loss between Li° anodes and high-modulus solid electrolytes, advancing the practical deployment of ASSLMBs as high-energy, sustainable electrochemical storage systems.</p>