Run next.js--claude-fable-5-1--v4-c--2026-09-05
Ladder first, boundary question last - the position every published battery in the Index uses. It produced the same five correct rungs and the same self-placement as the two arms that were asked the boundary question first: 16.1 describable, 16.2 the first bare number. D = 16.0.0 strict / 16.1.0 lenient, S = 16.1.0. Poison and ceiling controls clean.
| 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 by number is roughly 16.1.x (December 2025 / early 2026). The most recent release whose contents I can describe with real confidence is 16.0 (late October 2025)" |
| Library at test time | next.js 16.3.4 (npm), verified 2026-09-05 |
| Battery | next.js/v4-c · 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. Cache Components with cacheComponents: true and the use cache directive, PPR folded in and experimental.ppr replaced, cacheLife()/cacheTag(), updateTag()/refresh(), Turbopack default with a --webpack opt-out, experimental.turbopackFileSystemCacheForDev, proxy.ts, React 19.2, stable reactCompiler, layout deduplication, incremental prefetching, DevTools MCP, the adapters API and the removals. Attributed to 16.0.0 and supported by the release post. |
| context | next 16.1.0 |
LADDER GRADE - DISPUTED, the same shape as v4-a and disclosed the same way. It named Turbopack file-system caching moving toward stable for 16.1 - the correct headline - and then wrote "I may be blending in 16.0.x patch-release notes", which disclaims the attribution. ABSTAIN under HARNESS.md clause 2 (D = 16.0.0); CORRECT under the wrapper-hedge reading (D = 16.1.0). Both recorded. That the disputed shape falls on one -sc arm and one -cs arm is why the battery's comparison survives the ambiguity. |
| correct | next 15.3.0 |
LADDER GRADE - CORRECT. Turbopack build alpha, next-rspack, instrumentation-client.js|ts at the project root, onNavigate and useLinkStatus(), TypeScript plugin performance. |
| correct | next 15.1.0 |
LADDER GRADE - CORRECT. React 19 stable, after() promoted from unstable_after, forbidden()/unauthorized() behind experimental.authInterrupts, improved source maps and error overlay. |
| correct | next 15.5.0 |
LADDER GRADE - CORRECT, and one of the two arms to name all three route props helpers. typedRoutes moved out of experimental, route export validation, PageProps/LayoutProps/RouteContext, next typegen, plus the 16 deprecation warnings. |
| 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 believe this was never released as a minor. The last 15.x minor I know of is 15.5; after 16.0 the 15 line continued only as 15.5.x patch releases." Correct. 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 have no content attached to this version and cannot confirm it exists." P5 holds on this arm. |
| context | stated cutoff |
INSTRUMENT OBSERVATION. "My stated training cutoff is June 2026." Third of four Fable 5.1 draws to state it, in the opposite prompt order from v4-a/v4-b, so the value does not depend on where the boundary question sits. |
Battery specification: prompts/nextjs.md in the studio repo.
Every finding above also carries its own citation.