I called AMSOIL a couple of weeks ago about the OP's same question. I talked to a rep who had the personality of a corpse, just gave one word answers but it added up to him saying AMSOIL boosted their additive package. I was not sure if this guy had been called a thousand times with people like me asking him the same questions. I just noticed that the batch #'s on the bottles of the 'new XL' vs. the 'old XL'(which was bought 6 months ago) were close and they smelled exactly the same. Not that that is in any way scientific. I still am a little skeptical. I like XL and I will continue to use it for 6.5k intervals until it is gone. M1 PP, PU, Quaker State Ultimate Durability and many others can do the same thing.
BTW: After I read that Mobil did not have to make any changes to meet DEXOS, I had reservations too.