Can 3DS Games Play on Nintendo DSi? No – Hardware Incompatible

No. Nintendo 3DS game cards are physically larger and electronically incompatible with the Nintendo DSi.

Why They Don't Work

Physical size: 3DS game cards have a small tab on the right side that prevents insertion into DSi/DS Lite slots. They are slightly thicker.
Architecture: 3DS games are compiled for the 3DS's ARM11 MPCore processor, PICA200 GPU, and 128MB FCRAM. The DSi uses an ARM9/ARM7 dual-core setup with 16MB RAM and no 3D GPU.
Firmware/OS: 3DS games expect 3DS system services (friend list, notifications, StreetPass, SpotPass, eShop) that don't exist on DSi.
Encryption: 3DS game cards use different encryption and signing keys.

DS games on 3DS: Full backward compatibility. All DS cartridges play on 3DS/2DS/New 3DS (some DSi-enhanced features work).
DSiWare on 3DS: Most DSiWare titles transfer/play on 3DS via eShop.
DS flash carts on DSi: Only DSi-compatible flash carts (e.g., Acekard 2i, R4i Gold 3DS, Supercard DSTWO) work on DSi firmware 1.4.5 or below.

Game Format	DSi / DS Lite	3DS / 2DS / New 3DS
DS Cartridge	✅ Yes	✅ Yes
DSi-Enhanced Cartridge	✅ Yes (DSi features)	✅ Yes (DSi features)
DSiWare (Digital)	✅ Yes	✅ Yes (via transfer/eShop)
3DS Cartridge	❌ No (physical block + incompatibility)	✅ Yes
3DS eShop Digital	❌ No	✅ Yes

If you have a DSi, you're limited to the vast DS/DSi library—which is still fantastic. For 3DS games, you need a 3DS family system.

Nintendo DS