For decades graphite has been used as the anode material of choice for lithium batteries since porous carbons were believed to be inappropriate because of their high potential slope during lithiation as well as capacity losses due to intense formation of solid electrolyte interphase (SEI).However, in this work we demonstrate a microporous carbide-derived carbon material (HCmicro) to provide a high-capacity anode framework for lithium storage in all solid-state batteries. Half-cell measurements of HCmicro exhibit exceptionally high and reversible lithiation capacities of 1000 mAh g-1carbon utilizing an extremely long voltage plateau near 0 V vs. Li/Li+. The defined microporosity of the HCmicro combined well with the argyrodite-type electrolyte (Li6PS5Cl) suppressing extensive SEI formation to deliver high coulombic efficiencies. Preliminary full-cell measurements vs. NMC-cathodes (LiNi0.9Co0.05Mn0.05O2) obtained a considerably improved average potential of 3.76 V leading to a projected energy density as high as 443 Wh kg-1. 7Li Nuclear Magnetic Resonance spectroscopy was combined with ex-situ Small Angle X-ray Scattering and further electrochemical investigations to elucidate the storage mechanism of lithium inside the carbon matrix revealing the formation of extended quasi-metallic lithium clusters.