A state of eight: Iridium atoms insert into dioxygen to form iridium dioxide molecules in solid noble‐gas matrices. Annealing allows formation of the iridium dioxide superoxide complex [(η¹‐O₂)IrO₂], which isomerizes under IR irradiation to the iridium dioxide peroxide complex [(η²‐O₂)IrO₂]. These complexes photochemically rearrange to the more stable iridium tetroxide molecule with an iridium oxidation state of +VIII.