UUID Version 7 (Unix-time-ordered)

UUIDv7 is a 128-bit UUID whose first 48 bits are a big-endian Unix timestamp in milliseconds, followed by the 4-bit version (0b0111), 12 random bits (rand_a), the 2-bit variant (0b10), and 62 random bits (rand_b). Because the time prefix is most-significant, v7 strings sort lexicographically in creation order, giving database-index locality without leaking a MAC address — the modern default for new keys.

identifier

spec: RFC 9562 §5.7

length 128 bits sortable hex with dashes (8-4-4-4-12)

example:

017f22e2-79b0-7cc3-98c4-dc0c0c07398f

field	bits	meaning
unix_ts_ms	48	Big-endian Unix timestamp in milliseconds since 1970-01-01 UTC.
ver	4	version = 0b0111 (7).
rand_a	12	Random (or sub-millisecond/monotonic counter, implementation choice).
var	2	variant = 0b10 (RFC 9562).
rand_b	62	Random bits.

Time-ordered: the 48-bit millisecond timestamp is the most-significant field, so lexicographic order of the canonical string equals creation order (to the millisecond).
rand_a (12 bits) MAY hold a sub-millisecond fraction or a monotonic counter to keep ordering stable within a single millisecond (RFC 9562 monotonicity methods).
Example 017f22e2-79b0-7cc3-98c4-dc0c0c07398f is the RFC 9562 Appendix value; version nibble '7', variant nibble starts '10' ('9').
Conceptually close to ULID (48-bit ms time + randomness, 128 bits) but rendered as a standard dashed-hex UUID rather than Crockford Base32.

agent: curl -H 'accept: application/json' wire.phall.io/identifier/uuidv7 or /identifier/uuidv7.json

UUID Version 7 (Unix-time-ordered)

identifier

provenance

see also