GUID Version 1-8 - The Complete Comparison
Comprehensive comparison of all GUID versions (v1-v8). Understand the differences, use cases, security implications and performance characteristics of each version to choose the right one for your project.
RFC 4122 and RFC 9562
GUIDs are defined by IETF standards (RFCs). For many years, developers referenced RFC 4122 (published July 2005), but this document has been formally obsoleted by RFC 9562 (published May 2024). This comparison explains what changed, what stayed the same, and which RFC you should reference today.
TL;DR: RFC 9562 is the current GUID / UUID standard. RFC 4122 is still widely referenced but should be treated as a historical document.
Quick comparison
| Aspect | RFC 4122 (2005) | RFC 9562 (2024) |
|---|---|---|
| Publication date | July 2005 Nearly 20 years as the standard | May 2024 Current specification |
| Status | Obsolete Formally replaced by RFC 9562 since May 2024 | Current standard Authoritative reference |
| Primary role | Original GUID / UUID specification used by most legacy systems | Modern replacement that updates, clarifies and extends GUID / UUID definitions |
| Defined UUID versions | v1, v2 (reserved), v3, v4, v5 | v1, v2 (reserved), v3, v4, v5, v6, v7, v8 |
| v2 (DCE Security) | Reserved, not fully specified | Reserved, explicitly acknowledges DCE origin (still not fully specified) |
| Time-ordered UUIDs | Not addressed Sorting issues left to implementations | Explicitly addressed via v6 and v7 |
| Custom GUID / UUID layouts | Not supported | Supported via v8 (application-defined) |
| Ambiguity resolution | Several behaviors left implicit or unclear | Clarifies generation rules, intent and modern usage expectations |
| URN namespace | Defines urn:uuid: | Retains and reaffirms urn:uuid: |
| Security guidance | Limited discussion | Clearer warnings about predictability, privacy and misuse as secrets |
| Modern database considerations | Not explicitly addressed | Acknowledges ordering, index locality and real-world storage concerns |
| Recommended for new systems | No | Yes |
Key takeaways
- RFC 9562 supersedes RFC 4122: it is the official, current GUID / UUID standard.
- Nothing “breaks”: existing GUIDs / UUIDs generated under RFC 4122 remain valid.
- New versions matter: v6 and v7 directly address long-standing database and ordering problems.
- Documentation should cite RFC 9562: with optional mention of RFC 4122 for legacy context.
Practical advice for developers
- If you generate new GUIDs / UUIDs, reference RFC 9562 in documentation.
- If a library mentions “RFC 4122 GUIDs / UUIDs”, it usually still produces valid GUIDs / UUIDs — the wording is just outdated.
- Prefer v4 for simplicity and v6 or v7 for time-ordered IDs.
Frequently Asked Questions
Existing RFC 4122 GUIDs remain completely valid and don't need to be replaced. However, for new implementations, you should reference RFC 9562 as it's the current standard. The GUIDs / UUIDs themselves are backward compatible.
RFC 9562 introduces three new GUID / UUID versions (v6, v7, v8), provides better guidance on time-ordered GUIDs / UUIDs for database optimization, clarifies ambiguous behaviors from RFC 4122 and includes enhanced security considerations. All original GUID / UUID versions (v1, v3, v4, v5) remain unchanged.
For most applications, use GUID / UUID v4 for simplicity and randomness. If you need time-ordered identifiers for database performance, use GUID / UUID v7 (timestamp-based with random data). Use GUID / UUID v8 (discouraged because it is not widely supported) only if you need custom layouts for specific requirements.
Yes, RFC 9562 maintains full backward compatibility with RFC 4122. GUIDs / UUIDs generated under RFC 4122 (v1, v3, v4, v5) work exactly the same way in RFC 9562. The new standard only adds features and clarifications without breaking existing implementations.
RFC 4122 was officially obsoleted by RFC 9562 in May 2024. While RFC 4122 (published in 2005) is now considered a historical document, it served as the authoritative GUID / UUID standard for nearly 20 years and its core concepts remain valid.
Yes, it's recommended to update technical documentation to reference RFC 9562 as the current standard. You can mention RFC 4122 for historical context, but RFC 9562 should be your primary citation for accuracy and to align with modern best practices.
Conclusion
RFC 4122 laid the foundation for GUIDs / UUIDs and powered the web for nearly two decades. RFC 9562 modernizes that foundation without breaking compatibility, making it the correct reference point for all new GUID / UUID documentation and system design today.
Learn more
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