New insights into aluminum anion cluster reactivity with O were obtained through temperature-dependent kinetics measurements. Overall reactivity is controlled by a barrier at an avoided crossing where charge is transferred from the cluster to the O, mechanistically similar to what occurs as O approaches a bulk Al surface. Contrary to prior interpretations, spin conservation does not inhibit the reaction of clusters with an odd number of Al atoms. In fact, the only spin constraint in these systems is on the reactivity of even clusters due to repulsive surfaces, not previously recognized. Although the superatom nature of Al is manifest in its high electron binding energy (EBE), the mechanism of its reactivity is not special; it reacts with O as if it were a small piece of bulk Al. These experiments highlight the sensitivity of Al cluster reactivity with O to temperature and EBE, uncovering routes to industrial scale use of aluminum superatom-based materials.