Max UUID

What the Max UUID is

The Max UUID has all 128 of its bits set to one, which makes it the largest value the UUID space can hold. Like the Nil UUID it is not a version: RFC 9562 lists versions 1, 3, 4, 5, 6, 7 and 8, and defines Max alongside them as a special value.

When someone reaches for it

It is an edge case worth testing. If your code parses, stores, indexes or compares UUIDs, the all-ones value is the upper bound it has to survive, and it is the one most likely to expose an off-by-one in a hand-written parser or a column that is a byte too narrow.

It also works as an upper sentinel in a range scan: everything sorts before it, so it closes an interval without a special case.

What to watch out for

Max was only standardised in RFC 9562 in 2024. Older libraries may reject it as malformed while happily accepting the Nil UUID, so it is worth checking rather than assuming both are handled.