RFC 9562 (formerly RFC 4122) UUIDs

RFC 9562 (formerly RFC 4122) defines eight versions of UUIDs. Each version has different generation algorithms and properties. Which one you choose depends on your use-case. You can find out more about their applications on the specific page for that version.

Version 1: Gregorian Time: This version of UUID combines a timestamp, node value (in the form of a MAC address from the local computer’s network interface), and a clock sequence to ensure uniqueness. For more details, see Version 1: Gregorian Time.
Version 2: DCE Security: This version of UUID is the same as Version 1, except the clock_seq_low field is replaced with a local domain and the time_low field is replaced with a local identifier. For more details, see Version 2: DCE Security.
Version 3: Name-based (MD5): This version of UUID hashes together a namespace and a name to create a deterministic UUID. The hashing algorithm used is MD5. For more details, see Version 3: Name-based (MD5).
Version 4: Random: This version creates a UUID using truly-random or pseudo-random numbers. For more details, see Version 4: Random.
Version 5: Named-based (SHA-1): This version of UUID hashes together a namespace and a name to create a deterministic UUID. The hashing algorithm used is SHA-1. For more details, see Version 5: Name-based (SHA-1).
Version 6: Reordered Gregorian Time: This version of UUID combines the features of a version 1 UUID with a monotonically increasing UUID. For more details, see Version 6: Reordered Gregorian Time.
Version 7: Unix Epoch Time: This version of UUID combines a timestamp–based on milliseconds elapsed since the Unix Epoch–and random bytes to create a monotonically increasing, sortable UUID without the privacy and entropy concerns associated with version 1 and version 6 UUIDs. For more details, see Version 7: Unix Epoch Time.
Version 8: Implementation-Specific, Custom Format: This version of UUID allows applications to generate custom identifiers in an RFC-compatible format. For more details, see Version 8: Custom Format.