Which ink does the Epson Expression Home XP-4100 use?

The Epson Expression Home XP-4100 uses Epson 212 and Epson 212XL.

No. The Epson Expression Home XP-4100 is an inkjet, so it prints with liquid ink from a cartridge, not toner powder, and no toner cartridge fits it. If you were searching for Expression Home XP-4100 toner, the part you want is Epson 212 and Epson 212XL.

Yes. Besides the standard cartridges it accepts Epson 212XL. A high-yield XL holds more ink and costs less per page, which is worth it if you print often.

Epson can stop third-party ink working here with a firmware update, and it is the update rather than the cartridge that does it. Epson's own guide for the Expression Home XP-4100 says so in as many words: cartridges that functioned before a firmware update may not continue to function. Epson gives you the warning in advance, which is little use once the printer updates itself, so the defence is to decide when it updates. Turn automatic updates off before you fit a compatible, and keep a genuine cartridge in reserve for the day you do have to update.

Rated yields run from about 130 pages (Epson 212) to about 500 pages (Epson 212XL), depending on the cartridge. Real-world yield depends on how much you print and how much ink each page uses.

By list price the lowest cost per page here is the Epson 212XL at about 3.6 cents per page. A reliable compatible or remanufactured cartridge can lower that further.