The 5Ci FIPS is the same hardware as the standard YubiKey 5Ci, with one difference that matters on paper: it is validated to FIPS 140-3, the current US federal cryptographic standard. That validation is the whole reason to buy this version. If a contract, a framework, or an auditor requires a FIPS-validated authenticator, this is the box that ticks it. FIPS 140-2, the earlier generation, is being retired, so 140-3 is what to specify on new procurement.
Underneath the certification it is a full multi-protocol key on firmware 5.7: FIDO2/WebAuthn passkeys, FIDO U2F, PIV smart card, OATH-TOTP and OATH-HOTP, OpenPGP, YubiKey OTP, static password, and HMAC-SHA1 challenge-response. In practice that covers phishing-resistant sign-in to Microsoft 365 and Entra ID, and it satisfies the Essential Eight multi-factor control without staff typing a code.
The connector is the reason to choose the 5Ci over the rest of the range. One end is USB-C, the other is Lightning, which suits someone who works on a USB-C laptop but still carries an older Lightning iPhone or iPad and wants a single validated key for both. There is no NFC and no battery, so you plug the key in rather than tapping it against a phone.
It is crush- and water-resistant with no moving parts, built to live on a keyring for years. Be clear-eyed about the trade-off, though: Lightning is being phased out. If your phones have already moved to USB-C, you do not need the dual connector, and a plain USB-C key will cost less. Choose the FIPS variant only when the paperwork demands it, not by default.
Rolling it out means registering each key against your directory, whether that is Entra ID, Google Workspace, or another identity provider. Register a second key per person as a backup at the same time, because a single lost key means a lockout.
