The anthracene panels of two tetrahedral MII4L6 cages, where MII=CoII or FeII, were found to react with photogenerated singlet oxygen (1O2) in a hetero‐Diels–Alder reaction. ESI‐MS analysis showed the cobalt(II) cages to undergo complete transformation of all anthracene panels into endoperoxides, whereas the iron(II) congeners underwent incomplete conversion. The reaction was found to be partially reversible in the case of the 1‐FeII cage. The dioxygen‐cage cycloadducts were found to bind a set of guest molecules more weakly than the parent cages, with affinity dropping by more than two orders of magnitude in some cases. The light‐driven cycloaddition reaction between cage and 1O2 thus served as a stimulus for guest release and reuptake.