Max UUID — All-Ones Sentinel Value

The Max UUID (ffffffff-ffff-ffff-ffff-ffffffffffff) is all 128 bits set to 1. It was formally defined in RFC 9562 §5.10, published in May 2024 — it did not exist in the earlier RFC 4122.

What the Max UUID Is

ffffffff-ffff-ffff-ffff-ffffffffffff

• All 32 hex characters are f
• All 128 bits are 1
• No version digit, no variant bits — it is a raw sentinel value

The Max UUID is the direct opposite of the Nil UUID (00000000-0000-0000-0000-000000000000). Together they define the inclusive range of all possible UUID bit patterns.

Use Cases

Range bounds in queries:

The Max UUID is useful as an explicit upper bound when paginating or scanning UUID ranges:

-- All UUIDs in a time range using UUID v7's sortable prefix
SELECT * FROM events
WHERE id BETWEEN '018f0000-0000-7000-8000-000000000000'
             AND 'ffffffff-ffff-ffff-ffff-ffffffffffff'
ORDER BY id;

Sentinel for “greater than everything”:

In distributed systems that compare UUIDs, the Max UUID can represent infinity — a cursor position past all real records:

const MAX_UUID = 'ffffffff-ffff-ffff-ffff-ffffffffffff';

// "Give me everything after the last page" — returns nothing
const rows = await db.query(
  'SELECT * FROM orders WHERE id > $1 ORDER BY id LIMIT 50',
  [MAX_UUID],
);

Testing and boundary validation:

import uuid

NIL_UUID  = uuid.UUID(int=0)
MAX_UUID  = uuid.UUID('ffffffff-ffff-ffff-ffff-ffffffffffff')

# RFC 9562 §5.9 and §5.10 examples for documentation
assert str(NIL_UUID) == '00000000-0000-0000-0000-000000000000'
assert str(MAX_UUID) == 'ffffffff-ffff-ffff-ffff-ffffffffffff'

Database Storage

The Max UUID stores in any standard UUID column without issue:

-- PostgreSQL uuid column accepts Max UUID directly
INSERT INTO sentinels (id, label)
VALUES ('ffffffff-ffff-ffff-ffff-ffffffffffff', 'max');

-- Works in MySQL BINARY(16) via UUID_TO_BIN too
INSERT INTO sentinels (id, label)
VALUES (UUID_TO_BIN('ffffffff-ffff-ffff-ffff-ffffffffffff'), 'max');

Unlike the Nil UUID, the Max UUID is rarely stored as a real row — it is most often used as a query parameter for range bounds.

Max UUID vs Nil UUID

Validator Behaviour

Most UUID validators flag the Max UUID as a special case. The version digit at position 13 is f — not a valid version (1–8 are the only defined values). A well-implemented validator should:

1. Match the all-ones pattern and return “Max UUID” as a named result
2. Not reject it as “invalid” — it is valid per RFC 9562
3. Treat it as a sentinel, not a regular generated UUID

Related Resources

• RFC 9562 §5.10 — Max UUID definition
• Nil UUID — the all-zeros complement
• RFC 9562 replaces RFC 4122 — what changed
• UUID byte layout — all 128 bits explained