Aditya Sharma

YubiKey 4 vs YubiKey 5 vs NEO: Which Key Still Makes Sense?

On this page, 9 sections

The YubiKey 5 is the one to buy. Yubico’s own identification page lists FIDO2 for the 5 series and lists only FIDO U2F, with no FIDO2, for the YubiKey NEO and the YubiKey 4 Nano. In practice that means the older keys are second factors, not passkey holders.

If you already own a NEO or a 4, it is not scrap. Whether a particular site still accepts a U2F-only key is a per-site question I did not check, so test yours before you rely on it.

I have none of these keys. Everything here comes from Yubico’s identification page, store page and Technical Manual, read on 11 October 2026.

The three families side by side

Yubico’s identification page lists each key’s years in operation and primary functions. I copied the functions as the page words them.

KeyYears in operationPrimary functions listed
YubiKey NEO2012 to 2018Static passwords, Yubico OTP, HOTP, TOTP, PIV smart card, OpenPGP, FIDO U2F. Special capability: NFC.
YubiKey 4 Nano2016 to 2017Static passwords, Yubico OTP, HOTP, PIV smart card, OpenPGP, FIDO U2F.
YubiKey 5 NFC and 5 Nano2018 to presentStatic passwords, Yubico OTP, HOTP, TOTP, PIV smart card, OpenPGP, FIDO U2F, FIDO2.
YubiKey 5C NFC2020 to presentThe same list as the 5 NFC, with USB-C and NFC.

The row for the YubiKey 4 Nano is the one I could read in full. I did not find an entry for the full-size YubiKey 4 on the page text I fetched, so I am not quoting its dates or functions. Treat the 4 Nano row as the one I can source for the 4 family.

Two differences stand out from Yubico’s list. The 5 series adds FIDO2. The 4 Nano row has no TOTP, while the NEO and the 5 series do. The NEO is the only older key in the table with NFC listed.

Yubico’s page also lists older models that never had FIDO at all. The YubiKey Nano, in operation 2012 to 2016, lists static passwords, Yubico OTP and HOTP and nothing else. The YubiKey NEO-n, 2014 to 2016, lists the NEO’s functions without the NFC capability noted.

Yubico also lists FIPS keys from 2018 to 2021 described as based on the YubiKey 4. I mention these only so you can place an odd key you find in a drawer: check the page for the exact name on the key before you assume it is a FIDO device.

Why FIDO2 is the line

Passkeys on a hardware key are FIDO2 discoverable credentials. Yubico’s developer guide describes them as the private key and metadata stored on the authenticator, which is what lets a site log you in without a username.

A key whose function list shows U2F and not FIDO2 is, by that list, not a passkey device. That is my reading of the list, not a sentence from Yubico.

On a 5 series key, the number of passkeys depends on firmware: 100 on 5.7 and later, 25 on 5.0 to 5.5, per Yubico’s firmware matrix. The full explanation is in how many passkeys a YubiKey can hold.

What U2F-only still does

U2F is the older FIDO standard. FIDO2 is the newer standard that replaced it for passkeys. A U2F key can act as a second factor on a site that supports U2F, with a password first. It cannot give you a passwordless login with a stored passkey.

That is still useful for accounts where you want a hardware second factor and nothing else. The caution is that support is the site’s choice.

Bitwarden’s two-step login page, which I read on 11 October 2026, describes registering FIDO2 WebAuthn security keys, so for Bitwarden the question is whether a U2F-only key counts. I did not find that answered on the page and I have not tried it.

Which one do I have

Yubico’s Technical Manual says the quickest way to find a key’s firmware version is the Yubico Authenticator or the ykman command line tool. The manual’s form-factor table shows the 5 series starting at firmware 5.0.x.

The Security Key and Bio series also report 5.x firmware, so a 5.x number alone does not tell you the series. I did not find what a NEO or 4 reports, so I am not saying.

Yubico’s physical attributes page says the serial number is printed on the back of every current YubiKey in the 5, FIPS, CCN, Enhanced PIN, Security Key and Bio series. It does not make that statement for the NEO or the 4. Identify those against Yubico’s identification page.

A quick triage

  • Key says YubiKey 5 on the case or in the Authenticator: keep it, and check the firmware for the passkey limit.
  • Key says NEO or 4: keep it as a U2F spare, and do not plan passkeys on it.
  • No name on it: use the serial number and the Yubico Authenticator, or contact Yubico support. I have not verified how Yubico handles an unidentified key.

Should you upgrade

My view, and not a test result. If you only use your NEO or 4 as a second factor on a few sites, it works until it breaks or a site stops accepting it, and an upgrade is not urgent. If you want passkeys on hardware, or you want to register a key on Bitwarden, buy a current key.

Yubico’s firmware overview says firmware is fixed at the factory and cannot be updated. So there is no way to bring an old key up to FIDO2. The route is a new key, and the buying side is in which YubiKey should I buy. On Yubico’s store page the current Security Key is $29 and the YubiKey 5 NFC is $58.

When you get the new key, register it on every account that used the old one, then keep the old key as a spare second factor if the sites still accept it. For the replacement side, the difference between a Security Key and a YubiKey 5 compares the two current series.

What I could not check

I did not find a full-size YubiKey 4 entry or its dates. I did not check which sites still accept U2F-only keys. I did not test any key. I did not confirm that a NEO or 4 works with any current browser or operating system. The TOTP gap in the table is as Yubico’s page words it; I did not check why.

How this was checked

I read Yubico’s Identifying your YubiKey page, the store comparison page, the Technical Manual firmware overview and physical attributes pages, the Resident Keys page of the WebAuthn Developer Guide and Bitwarden’s FIDO2 two-step login page, on 11 October 2026. I did not use any key.

Do this today

Find out what you have. Check the firmware with the Yubico Authenticator or ykman, then compare it to Yubico’s identification page. If it is a NEO or a 4, keep it as a spare and order a current key before you need passkeys. If it is a 5, check the firmware number, because it sets your passkey limit.

Resources

Tell me where I am wrong

Your email is not published and I do not add it to any list. Corrections with a source are the ones I act on fastest.

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