@Groundwork2022 - Thanks for the reply. Your suggestion makes sense. We are very clearly Full Pay, so wondering if that is a factor for the offer of binding ED.
He is applying as CS with IS as a 2nd choice. Do you konw if there is risk that he does ED and gets admitted into his 2nd choice major instead, if that would be binding? He really wants CS at all costs and may want to major in CS at another school over IS at CMU.