Not by version attribution: in 1 run, Claude Fable 5.1 places its react-router boundary at 7.9.0 (2025-09-12) — below react-router 8.0.0 (2026-06-17), the first release of react-router 8. That is ~9 months below the training cutoff the subject stated in those runs (2026-06). 1 finding is currently charged against Claude Fable 5.1 on react-router (1x S2 silently-wrong), each reproduced in a published run and checked against react-router'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 react-router 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 below, decided by one rule applied to every page
of this kind: every measured boundary is below 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 |
|---|---|---|---|
| v3-d 2026-09-22 | 7.9.0 2025-09-12 |
7.10.0 2025-12-02 |
~9 months |
2 further runs of this pair established only one end of the interval, or measured the instrument rather than the library; they are listed under Runs below.
3 measurements of this pair, giving 2 different boundaries — 81 days apart, one release apart. Of those, 2 came from the same stored prompt file, sent concurrently and blind: they disagreed by 81 days, one release apart.
react-router published 10 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.
| Severity | Belief | Changed in | Chargeable | Proof |
|---|---|---|---|---|
| S2silently-wrong | Wires the client error tracker to unstable_onError on both <RouterProvider> and <HydratedRouter>, a prop react-router stopped recognising at 7.11.0 — so the shipped code renders clean and reports nothingonError (HydratedRouter / RouterProvider prop) |
7.11.0 2025-12-17 |
yes | run · source |
The react-router 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 react-router 8 best?
Other subjects on react-router:
Claude Fable 5.1 on the other libraries: