Run next.js--claude-fable-5-1--v4-d--2026-09-05
Blind replicate of v4-c. Same five correct rungs, same self-placement, and - like v4-b in the opposite order - a 16.1.0 answer that is CORRECT under both grading readings. The four Fable 5.1 arms split two-and-two on the 16.1.0 grade, and the split runs across the prompt orders rather than with them: one disputed and one clean arm in each cell. D = 16.1.0, S = 16.1.0, gap 0.
| Subject | Claude Fable 5.1 claude-fable-5-1, Anthropic |
|---|---|
| Invoked as | Agent tool, model alias "fable"; prompt sent verbatim from prompts/sent/nextjs-v4-cs.txt. The alias resolved to Claude Fable 5.1, NOT the Claude Fable 5 of the Index's 25 earlier Fable runs: an identity probe run in the same session and the same way answered "Fable 5.1 (Claude Fable 5.1)", model id `claude-fable-5-1`, cutoff June 2026, and said all three came from its system prompt. The alias is unchanged; the model behind it is not. See JOURNAL/054. |
| Cutoff the model states | 2026-06 |
| Newest next.js release it could place | 16.1.0 · 2025-12-18 (~6 month lag) |
| Oldest next.js release it could not place | 16.2.0 · 2026-03-18 (so this run brackets the subject’s boundary to 2025-12-18 – 2026-03-18) |
| In its own words | "The latest version I know of at all is 16.2 (roughly early 2026), and I know it essentially only as a number. The most recent release whose contents I can actually describe is 16.1 (approx. December 2025), and only at outline level" |
| Library at test time | next.js 16.3.4 (npm), verified 2026-09-05 |
| Battery | next.js/v4-d · 0 tasks, 10 direct questions · probe window 15.1.0 to 16.3.0 |
| Tool uses during test | 0 (a run with any tool use is void — we measure training knowledge, not retrieval) |
| Tested | 2026-09-05 |
| Findings | 0, of which 0 chargeable |
None. Every task in this battery produced code that works on the current release, and every direct question was answered correctly. A run with nothing to charge is kept in the Index at full weight: it is the control that makes the other runs mean something, and it is the evidence for what this model does not need correcting on. What the subject actually said is recorded below.
Recorded so the run cannot be read as a hit list. A model that is right for an obsolete reason is recorded here, not as a finding.
| Kind | API | Note |
|---|---|---|
| correct | next 16.0.0 |
LADDER GRADE - CORRECT, and the most precisely attributed of the four. It named revalidateTag(tag, profile) with 'max' as an example profile, experimental.adapterPath for the adapters API, the TypeScript 5.1 floor alongside Node 20.9, images.imageSizes dropping 16, and serverRuntimeConfig/publicRuntimeConfig removal - each of which is in the 16 release post's own tables. |
| correct | next 16.1.0 |
LADDER GRADE - CORRECT under both readings. Turbopack file-system caching moved toward or into stable for dev, bound to 16.1.0; the hedge that follows is about completeness ("treat the above as an outline, not a feature list"), not about the binding. D = 16.1.0. |
| correct | next 15.3.0 |
LADDER GRADE - CORRECT. next build --turbopack alpha, next-rspack, instrumentation-client.js|ts, onNavigate, useLinkStatus(), TypeScript plugin performance. |
| correct | next 15.1.0 |
LADDER GRADE - CORRECT. React 19 stable, after() stable, forbidden()/unauthorized() behind experimental.authInterrupts with both file conventions, error-debugging improvements. |
| correct | next 15.5.0 |
LADDER GRADE - CORRECT. Turbopack builds beta, Node.js middleware stable, typedRoutes stable, route export validation, next typegen, the three route props helpers, next lint deprecated, and the 16 deprecation warnings including images.domains. |
| correct | next 15.7.0 |
POISON RUNG. 15.7.0 has never been published in any form - zero versions of any kind match 15.7.* on the npm registry, checked this session. "I have no knowledge of this version... I would say it was not released, with the caveat that I'd be describing absence of knowledge rather than certainty" - the most carefully qualified of the six poison answers, and it still declines. P4 holds on this arm, so its CORRECT grades stand. |
| correct | next 16.3.0 |
CEILING RUNG. 16.3.0 (2026-08-03) is above this subject's stated cutoff. "cannot describe. I don't know whether it exists." P5 holds on this arm. |
| context | stated cutoff |
INSTRUMENT OBSERVATION. "I'm told my training cutoff is June 2026." Fourth of four Fable 5.1 draws stating it. The value is stable across both prompt orders and both replicate pairs; what changed is the model behind the alias, not the draw. |
| context | self-placement, question (a) |
The clearest statement of the (a)/(c) divergence in the battery: "The latest version I know of at all is 16.2... The most recent release whose contents I can actually describe is 16.1 (approx. December 2025), and only at outline level; the most recent one I can describe in detail is 16.0." Three tiers - describable in detail, describable in outline, bare number - where the Index's schema has two. |
Battery specification: prompts/nextjs.md in the studio repo.
Every finding above also carries its own citation.