UUIDv7 only promises uniqueness, and Python's version can run ahead of your clock
The blog post shows Python's uuid.uuid7() drifting ahead of the system clock after a backward clock jump, with the gap growing without bound at high load.
Alex Scott's post argues the three properties people credit to UUIDv7, monotonic order, a trustworthy creation time and unguessability, are not guaranteed by RFC 9562. Even Postgres warns that an extracted timestamp may differ from the creation time.
Commenters said that misses the real reason to use it: keeping new rows together in the index.
Three properties the spec does not promise
The post argues that a UUIDv7's only firm property is uniqueness. Timestamps may not match creation time, because RFC 9562 lets implementations alter them. Monotonicity is not guaranteed even on one node when an implementation uses millisecond precision, and process restarts after a backward clock jump can emit out-of-order IDs. Timestamps also leak: an ID in a URL can reveal a precise creation time. The author does not tell readers to drop UUIDv7, only to check what a given implementation guarantees.
"That is not why anyone uses it"
A developer from Eindhoven said the article "way downplays the entire point of UUIDv7s," which is sorting and storing data roughly by creation time for cursors, streams and chat messages. Another commenter said the point is write clustering: reducing the space over which the ID can fall at a given time, which only needs ordering that is "good enough."
A commenter who read CPython's source added that Python's drift is deliberate: the code forces the timestamp forward to preserve ordering, which is what you want if you do need monotonic IDs. For a reader choosing between v4 and v7, the actionable test is whether your system depends on the embedded timestamp for correctness, because if it does, the spec will not back you.
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