This article applies to all YubiKey devices.
To identify the version of YubiKey you have, use the YubiKey Personalization Tool, which works with any key as long as it is not a U2F-only device, to identify your YubiKey. Because the 4th generation YubiKey, the YubiKey 4 looks like the YubiKey Edge, this is one way to tell the two keys apart. Download the YubiKey Personalization Tool from our Downloads page. The YubiKey 4 will have a firmware version of 4.2.6 or later. To identify what type of YubiKey you have, see Identifying Your YubiKey.