RFC 9562 — The Modern UUID Standard Explained

What This Video Covers

RFC 9562 overview videos walk through the IETF standard that replaced RFC 4122 in May 2024 — covering why the old standard needed updating, what each new version adds, and what deprecation means in practice.

Skill level: Beginner to intermediate Best for: Developers who have been using UUID v4 and want to understand whether and when to adopt v7

Key Concepts You Will Learn

1. Why RFC 4122 was replaced

RFC 4122 (2005) defined UUID versions 1–5. Its limitations that RFC 9562 addressed:

• v1 exposed MAC addresses — a machine fingerprint and privacy leak
• v1’s timestamp fields were not in lexicographic sort order (time_low came first)
• No time-sortable version suitable for modern database primary keys
• No sentinel for “maximum value” (only Nil UUID existed)

2. UUID v6 — reordered v1

v6 takes v1’s 60-bit Gregorian timestamp and rearranges the fields so the UUID is lexicographically sortable. It is a bridge for systems already on v1 — same clock precision (100ns), same MAC address node field, but sortable. Not recommended for new systems — use v7 instead. See Time-Based UUID for the field-by-field comparison.

3. UUID v7 — the modern default

v7 uses a clean 48-bit Unix millisecond timestamp, no MAC address, and 74 bits of randomness. It is lexicographically sortable, collision-safe, and privacy-respecting. The recommended choice for database primary keys in 2026. PostgreSQL 18 ships a native uuidv7() function; Python 3.13 adds uuid.uuid7() to the standard library.

4. UUID v8 — application-defined layout

v8 is a blank canvas: only the 4-bit version and 2-bit variant fields are specified. The remaining 122 bits are application-defined. Use it when you need to embed custom metadata — shard IDs, region codes, custom-precision timestamps — while keeping the standard UUID column type. See UUID v8 — Custom Layout.

5. The Max UUID sentinel

Max UUID (ffffffff-ffff-ffff-ffff-ffffffffffff) is all 128 bits set to 1 — the complement of the Nil UUID. Useful as an explicit upper bound in range queries and pagination cursors.

6. Version field position

The version is the single hex digit at position 13 of the UUID string — the first character of the third group (xxxxxxxx-xxxx-Vxxx-xxxx-xxxxxxxxxxxx). Reading this digit tells you which RFC you are dealing with. See UUID Version field and the UUID Decoder tool.

Related Reading

• RFC 9562 replaces RFC 4122 — what changed
• All UUID versions explained (v1–v8)
• Time-Based UUID — v1, v6, and v7
• Max UUID — the all-ones sentinel
• UUID Version field
• UUID v8 — Custom Layout for Application IDs
• UUID Byte Layout — 128-bit structure

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Validate a UUID from the Video

Use the UUID Validator to check any UUID from a video example — it shows version, variant, and whether it follows RFC 9562.