For all of our YubiKeys (YubiKey 4/YubiKey 4 Nano/YubiKey 4C, YubiKey NEO/NEO-n, YubiKey Edge/Edge-n, and YubiKey Standard/Nano), there are two "configuration slots" on each YubiKey. You can program each slot with a single credential, such as one for OTP and one for OATH-TOTP. All keys also support static password or challenge-response. For the keys that support FIDO U2F, you can have an unlimited number of U2F credentials on the YubiKeys that support that protocol. These keys are the YubiKey 4/YubiKey 4 Nano, YubiKey NEO/NEO-N and YubiKey Edge/Edge-n plus the FIDO U2F Security Key. The YubiKey 4/YubiKey 4 Nano/YubiKey 4C, and YubiKey NEO/NEO-n also can store up to 28 OATH-TOTP credentials in addition to the pre-configured Yubico One-Time Password that is configured in slot 1. Finally, the YubiKey 4/YubiKey 4 Nano/YubiKey 4C and YubiKey NEO/NEO-n can also store a smart card (PIV) credential and the YubiKey 4/YubiKey 4 Nano/YubiKey 4C can be configured for touch-to-sign for code signing. For more information about the functions of the keys and their current availability, see our products page.