My XDS Mod.2 came with one 7-round magazine and one extended 9-round magazine. My favorite magazine for the XDS Mod.2 is the 8-round magazine available on the Springfield website. The 9-rounder stuck out just far enough to make the gun print, and the 7-rounder leaves my pinky hanging off. The 8-rounder is the ultimate compromise because it offers a full-grip without printing.
When you register your new firearm's warranty with Springfield, they will allow you to buy additional magazines at a discount for 90 days. It's a great time to pick up extra mags at a decent price.