Partly: in 1 run, Claude Opus 5.5's zod attribution reaches 4.1.0 (2025-08-23), inside zod 4, and the subject states it stops there — zod was at 4.6.5 when this index last tested it (2026-09-27). Claude Opus 5.5's stated zod end at 4.1.0 is equivocal: in the same draw it placed the content of zod 4.2.0 (2025-12-15) correctly while declining to call that a description, so its attribution may reach 4.2.0. That is ~10 months below the training cutoff the subject stated in those runs (2026-06). No finding is currently charged against Claude Opus 5.5 on zod and no probe in the 1 run published here recorded a miss; one answer was recorded as imprecise and not charged. Read the boundary precisely: it is the newest release whose contents the model can correctly attribute to that release, not the newest zod feature it can use. Past it a model often writes working code with a newer API while naming the wrong release for it.
Answer class inside, decided by one rule applied to every page
of this kind: every measured boundary is at or above the first release of the major named in the question. Every figure below is read from
the dataset at build time; nothing on this page is written by hand.
| Battery | Newest release it can place | Oldest it cannot | Lag vs stated cutoff |
|---|---|---|---|
| v8 2026-09-27 | 4.1.0 2025-08-23 |
4.2.0 2025-12-15 |
~10 months |
One measurement of this pair, all giving the same boundary. No two of them were drawn from an identical prompt, so the spread mixes prompt differences with draw variance.
zod published 5 minor or major releases in the twelve months before this model’s stated cutoff, which is the scale a spread should be read against.
Nothing is charged and no probe in the runs below recorded a miss; 1 answer was recorded as imprecise and not charged.
The zod correction pack states what is true now for each corrected fact, with a primary-source citation, as markdown you can paste into a rules file (raw). What a correction pack measurably changed when one was tested — a pre-registered run on prisma and zod — is on the benchmark page, including where it changed nothing.
All of them at once: Which Claude model knows zod 4 best?
Other subjects on zod:
Claude Opus 5.5 on the other libraries: