The Nintendo DSi XL features larger screens, and a greater overall size, than the original DSi. It is the fourth DS model, the first to be available as a pure size variation. Iwata said that cost restraints had, until then, limited the screen size and multiplayer aspects of portable game consoles, and that the DSi XL offers "an improved view angle on the screens", which makes it the first "portable system that can be enjoyed with people surrounding the gamer." He argued that this introduces a new method of playing portable video games, wherein those "surrounding the game player can also join in one way or the other to the gameplay." While the original DSi was specifically designed for individual use, Iwata suggested that DSi XL buyers give the console a "steady place on a table in the living room," so that it might be shared by multiple household members.

The DSi XL is the longest, widest and heaviest DS model. The console features two 4.2-inch (110 mm) wide-viewing-angle LCD screens with the same resolution as the smaller model. It has improved battery life over the DSi on all brightness settings; for example, batteries last 13–17 hours at the dimmest setting. The handheld is outfitted with identical speakers contained in larger speaker enclosures, enabling them to produce louder sound. The hinges stop the screen at 120° in addition to the original DSi's position of 155° to allow easier table-top viewing. The DSi XL is bundled with two longer styli, one of which is thicker, rounded, and pen-like, and does not fit inside the unit.

The DSi XL has a matte surface, and the exterior of its top panel is coated with a gloss finish. It is available in eight two-toned colors, varying by region such as white, green, red, yellow, and pink. Two special-edition models were released: those for LovePlus+ and the 25th anniversary of Super Mario Bros. Flipnote Studio and the Nintendo DSi Browser come pre-installed with the DSi XL, alongside other, region-specific software.