XP90 is stock and no upcharge from what I can tell in custom catalog. You are good to go! Enjoy!!

I play the AP2-716 in an XP90 reg shaft. Got fit for them. Love them. Didn't pay anything extra when I ordered them.

As previously answered, yes. Fun fact, any shaft, stock or custom, can be ordered for any head in that category. Often there are custom options that have no upcharge, when you look at the Titleist handbook for customization. As a LH senior golfer, no standard/stock set on the rack fits me, so I work with a on-course fitter and not a retailer promoting "stock sets" that they have to special order for me anyway. For me, any custom shaft with no upcharge is on my list of "stock" shafts.