User blog comment:AntiScootaTwo/Call of Duty Wiki News - August 9th, 2015/@comment-402843-20150810042933/@comment-1905698-20150815235851

It's obvious the M8A1 is the "finished" version of XM8, for several reasons (name, model, game files). Things like that may go differently in the universe; maybe they refounded the experiment and found a solution to the common problem between now and 2025, which I recall was the plastic parts melting.