{
  "id": "identifier/uuidv7",
  "family": "identifier",
  "slug": "uuidv7",
  "title": "UUID Version 7 (Unix-time-ordered)",
  "summary": "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.",
  "kind": "identifier",
  "aliases": [
    "UUID v7",
    "time-ordered UUID",
    "version 7 UUID",
    "sortable UUID"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://www.rfc-editor.org/rfc/rfc9562#section-5.7",
  "source_version": "RFC 9562 §5.7",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "identifier/uuidv4",
    "identifier/ulid",
    "identifier/uuidv1"
  ],
  "ext_type": "identifier@1",
  "ext": {
    "spec": "RFC 9562 §5.7",
    "example": "017f22e2-79b0-7cc3-98c4-dc0c0c07398f",
    "bit_layout": [
      {
        "field": "unix_ts_ms",
        "bits": 48,
        "meaning": "Big-endian Unix timestamp in milliseconds since 1970-01-01 UTC."
      },
      {
        "field": "ver",
        "bits": 4,
        "meaning": "version = 0b0111 (7)."
      },
      {
        "field": "rand_a",
        "bits": 12,
        "meaning": "Random (or sub-millisecond/monotonic counter, implementation choice)."
      },
      {
        "field": "var",
        "bits": 2,
        "meaning": "variant = 0b10 (RFC 9562)."
      },
      {
        "field": "rand_b",
        "bits": 62,
        "meaning": "Random bits."
      }
    ],
    "length_bits": 128,
    "sortable": true,
    "encoding": "hex with dashes (8-4-4-4-12)",
    "notes": [
      "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."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}