Herein, we report the molecular engineering of anion-fluxing polymeric metal phthalocyanines (MTPs) by controlling the types of metal centers and incorporating lithiophilic linkers to achieve ultrastable Li metal batteries. Spectroscopic characterization, cryogenic transmission electron microscopy, and computational simulations demonstrate that the Co–N4 sites of Co in the incorporated MTP (CoTP) facilitate the local accumulation and directional flux of TFSI anions, inducing the formation of uniform, dense LiF-rich solid electrolyte interphases. As a result of this interfacial chemistry, symmetric cells with CoTP@CC–Li exhibited outstanding cycling stability, exceeding 2500 hours at 1 mA cm−2 and 1 mAh cm−2. CoTP@CC–Li||LiFePO4 full cells operated stably for over 600 cycles under fast charge/discharge conditions, with a high-mass-loading cathode of 20 mg cm−2. CoTP@CC–Li||LiFePO4 pouch cells demonstrated stable cyclability under demanding practical conditions, including a low N/P ratio of 2.5, high cathode mass loading (23.53 mg cm−2), and lean electrolyte usage (5 g Ah−1). Furthermore, CoTP@CC-enabled anode-free full cells achieved exceptional stability over 500 cycles, even under stringent conditions (NCM811 mass loading of 20 mg cm−2 and lean electrolyte usage of 3 g Ah−1). These results highlight the effectiveness of the anion-flux interfacial engineering strategy for enabling stable and reversible Li deposition under demanding conditions.