{
  "id": "identifier/ksuid",
  "family": "identifier",
  "slug": "ksuid",
  "title": "KSUID (K-Sortable Unique Identifier)",
  "summary": "A KSUID is a 160-bit identifier: a 32-bit Unix timestamp (in seconds, offset to a 2014-05-13 epoch) followed by a 128-bit random payload, rendered as 27 characters of base62. The timestamp prefix makes KSUIDs roughly time-sortable, and the 32-bit second-resolution epoch offset buys over a century of range. Created by Segment.",
  "kind": "identifier",
  "aliases": [
    "K-Sortable Unique Identifier",
    "Segment KSUID"
  ],
  "status": "de-facto",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://github.com/segmentio/ksuid",
  "source_version": "segmentio/ksuid (unversioned)",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "identifier/ulid",
    "identifier/uuidv7"
  ],
  "ext_type": "identifier@1",
  "ext": {
    "spec": "KSUID (github.com/segmentio/ksuid)",
    "example": "0ujtsYcgvSTl8PAuAdqWYSMnLOv",
    "bit_layout": [
      {
        "field": "timestamp",
        "bits": 32,
        "meaning": "Unix UTC seconds MINUS the KSUID epoch offset 1400000000 (2014-05-13 16:53:20 UTC)."
      },
      {
        "field": "payload",
        "bits": 128,
        "meaning": "Cryptographically random payload."
      }
    ],
    "length_bits": 160,
    "sortable": true,
    "encoding": "base62 (0-9 A-Z a-z), fixed 27 characters",
    "notes": [
      "20 bytes binary (4-byte timestamp + 16-byte payload) -> always 27 base62 characters, fixed width and lexicographically sortable by timestamp.",
      "Epoch offset: KSUID timestamp = unix_seconds - 1400000000, shifting the usable range to ~2014..2150 instead of wasting the low values.",
      "Second resolution (coarser than ULID/UUIDv7's millisecond), so ordering within the same second relies on the random payload (not strictly monotonic).",
      "Example 0ujtsYcgvSTl8PAuAdqWYSMnLOv is the README sample (timestamp 107608047 -> 2017-10-09, payload B5A1CD34B5F99D1154FB6853345C9735)."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}