Do DS Lite Games Fit in a 3DS XL? Yes - DS & 3DS Cards Are Same Size

Yes, they fit perfectly. DS game cards (used in DS Lite) are physically identical in size and shape to 3DS game cards. The 3DS XL slot accepts both DS and 3DS cards.

Important clarification: The original source incorrectly stated they don't fit. The confusion often stems from the reverse: 3DS games do NOT work in a DS Lite (the cartridge has a small tab preventing insertion). But DS games work fine in any 3DS family system (3DS, 3DS XL, 2DS, New 3DS).

So if you have a DS Lite game cartridge, it will work in your 3DS XL. Enjoy your backward compatibility!