Partly: in 3 runs, Claude Opus 5.5's next.js attribution reaches 16.0.0 (2025-10-22) and 16.1.0 (2025-12-18), inside next.js 16, and stops there — next.js was at 16.3.6 when this index last tested it (2026-09-28). That is ~6 to ~8 months below the training cutoff the subject stated in those runs (2026-06). 1 finding is currently charged against Claude Opus 5.5 on next.js (1x S2 silently-wrong), each reproduced in a published run and checked against next.js's own release notes. Read the boundary precisely: it is the newest release whose contents the model can correctly attribute to that release, not the newest next.js 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.
3 measurements of this pair, giving 2 different boundaries — 57 days apart, one release apart. Of those, 2 came from the same stored prompt file, sent concurrently and blind: they agreed exactly.
next.js published 4 minor or major releases in the twelve months before this model’s stated cutoff, which is the scale a spread should be read against.
“Chargeable” means the change was published before this model’s own stated cutoff, so it had the opportunity to know it.
The next.js 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 next.js 16 best?
Other subjects on next.js:
Claude Opus 5.5 on the other libraries: