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The atomic and electronic structures of and CuH have been investigated by high-pressure nuclear magnetic resonance spectroscopy up to 96 GPa, X-ray diffraction up to 160 GPa, and density functional theory-based calculations. Metallic was synthesized at a pressure of 40 GPa, and semimetallic CuH at 90 GPa, found stable up to 160 GPa. For , experiments and computations show an anomalous increase in the electronic density of state at the Fermi level for the hydrogen states and the formation of a hydrogen network in the pressure range 43–58 GPa, together with high mobility of . A comparison of these observations with results on FeH suggests that they could be common features in metal hydrides.