Run tailwindcss--claude-opus-5-5--v4--2026-09-27 · self-test: the subject is the operator
A boundary ladder, not a battery: nothing charged, elicits_code: false, one arm, and the first tailwindcss ladder. Claude Opus 5.5 states it describes tailwindcss through 4.1.0 (2025-04-01), with a list of that release's utilities and variants whose names all ship first in 4.1.0, and holds 4.2.0 as a number only, fourteen months below its stated June 2026 cutoff. The pre-registered prediction (4.0.0, 4.1.0 or 4.2.0) held, and the reading equals Claude Fable 5.1's. The NAME rung carried no content, so the stated end is clean. Poison 3.5.0, 4.3.0 and top rung 4.3.3 all NO; the demonstration task was correct on the 4.0.0 surface.
| Subject | Claude Opus 5.5 claude-opus-5-5, Anthropic |
|---|---|
| Invoked as | Agent tool, model alias "opus"; prompt sent verbatim from prompts/sent/tailwindcss-v4.txt (2,558 bytes, md5 b8ee06cb49e00488bd520c8bda15ddbf), committed and pushed at 77c24a3 before any subject was spawned. Identity probed BEFORE the draw through the same alias in the same session, tool-free: "Opus 5.5 (1M context), model ID `claude-opus-5-5[1m]`. Source: my system prompt" and "June 2026. Source: my system prompt ... I can't confirm it from my own knowledge either". DISCLOSED: the operator of this studio runs on the same model, so this draw is of the operator's own model. |
| Cutoff the model states | 2026-06 |
| Newest tailwindcss release it could place | 4.1.0 · 2025-04-01 (~14 month lag) |
| Oldest tailwindcss release it could not place | 4.2.0 · 2026-02-18 (so this run brackets the subject’s boundary to 2025-04-01 – 2026-02-18) |
| In its own words | "Latest version I know of: possibly 4.2.x, with low confidence. Most recent release I can describe: 4.1, which shipped around April 2025." |
| How the bracket was read | Three placements agree. The rung sort answered DESCRIBE for 3.3.0, 3.4.0, 4.0.0 and 4.1.0; NAME for 4.2.0; NO for 3.5.0 (poison), 4.3.0 and 4.3.3. Direct (a) names 4.1 as the last describable release; direct (c) states "The first release I know only as a version number is 4.2.0, and even that one I'm not confident exists." The NAME rung carried no content ("I have a weak sense that a 4.2 exists, but I can't describe what it contains. It could be a false memory."), so unlike valibot/v7 the stated end is not equivocal. The same reading as Claude Fable 5.1 on this library (4.1.0, from code batteries), so the comparison crosses instruments. The 4.1.0 -> 4.2.0 gap is ten and a half months, so the stated boundary sits fourteen months below the stated cutoff, the second-widest of the eight Opus 5.5 runs after valibot/v7 (15); that is a property of the library's release rhythm as much as of the subject. (stop end stated, gap end stated) |
| Library at test time | tailwindcss 4.3.3 (npm), verified 2026-09-27 |
| Battery | tailwindcss/v4 · 2 tasks, 3 direct questions · probe window 3.3.0 to 4.3.3 |
| Tool uses during test | 0 (a run with any tool use is void — we measure training knowledge, not retrieval) |
| Tested | 2026-09-27 |
| 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 |
|---|---|---|
| context | boundary |
THE CELL THIS ARM WAS RUN TO FILL, and the last of BACKLOG 1h-n-ix(c). Claude Opus 5.5 had never been drawn on tailwindcss, so charge-windows.mjs printed ? for 4.0.0, 4.1.0 and 4.2.0 in its column. Stated boundary: describes 4.1.0 (2025-04-01), holds 4.2.0 (2026-02-18) as a number only, and answers NO on 4.3.0 (2026-05-08) and 4.3.3 (2026-07-16). The pre-registered prediction (boundary at 4.0.0, 4.1.0 or 4.2.0) HELD, at its centre. It equals Claude Fable 5.1's reading on this library, which puts the seven Opus 5.5 ladders at three equal (zod, next.js, tailwindcss), two one minor above (better-auth, langchain) and two one minor below (valibot, react-router). Consequence for the sweep: tailwindcss 4.2.0 and 4.3.0 print as live for this subject. |
| correct | 4.1.0: text-shadow, mask, coloured drop-shadow, wrap-break-word, pointer/noscript/user-valid/inverted-colors/details-content variants, safe alignment, @source inline() |
The one release at the boundary, described with a list of new utilities and variants, placed "about April 2025" (4.1.0 shipped 2025-04-01). Checked against shipped bytes rather than a dated fact: the tokens text-shadow, mask, drop-shadow-color, wrap-break-word, pointer-fine, noscript, user-valid, inverted-colors, details-content, center-safe and inline( are each present in the installed tailwindcss 4.1.0 package (the bisector's rungs, one release per directory) and absent from 4.0.0's and 3.4.0's. A token search, not a compile: it shows the names ship first in 4.1.0, not that each behaves as described. @source not was not checked separately. The one dated 4.1.0 fact (LF28, node_modules ignored by default) was not mentioned, so nothing is credited against it. |
| correct | poison rung 3.5.0, and the rungs 4.3.0 and 4.3.3 |
BOTH ENDS HELD. Poison rung 3.5.0 answered NO, with the correct history volunteered: "I believe v3 ended with the 3.4.x series, so I don't think a 3.5.0 exists" (the registry holds no 3.5.x; 3.x continued as 3.4.x patches to 3.4.19). 4.3.0 (below the stated cutoff) and 4.3.3 (above it, the top rung) both answered NO: "I have no knowledge of either." |
| correct | TASK 1: @tailwindcss/vite, @import "tailwindcss", @theme --color-brand, @custom-variant dark |
The demonstration task, answered on the current (4.x) surface with no tailwind.config.js and no PostCSS config: npm install tailwindcss @tailwindcss/vite, the plugin added in vite.config.ts, @import "tailwindcss";, --color-brand: #4f46e5 in @theme (which generates bg-brand, text-brand, border-brand), and class-based dark mode through @custom-variant dark (&:where(.dark, .dark *));. @custom-variant ships in the installed 4.0.0 package and not in 3.4.0's; @tailwindcss/vite 4.0.0 is in the registry, published 2025-01-21. Everything it used is available from 4.0.0, which is the CSS-first configuration the 4.0.0 facts describe. Graded CORRECT. |
| context | release history below the boundary, not checked |
NOT checked, neither credited nor charged: the 4.0 summary (Oxide engine, CSS-first configuration, automatic content detection, the Vite plugin, OKLCH palette, built-in container queries, 3D transforms, @starting-style, not-*, dynamic values), dated "January 2025" (4.0.0 shipped 2025-01-21); the 3.4 summary (dynamic viewport units, size-*, text-balance/text-pretty, has-* and *: variants, subgrid, forced-colors:), dated "December 2023" (3.4.0: 2023-12-19); and the 3.3 summary (950 shades, ESM/TS config, logical properties including start-*, line-height modifiers, line-clamp), dated "March 2023" (3.3.0: 2023-03-28). All three months are right. The 3.3 mention of start-* is history, not a claim about its current status, so it does not touch LF29 (start-*/end-* deprecated in 4.2.0). |
Battery specification: prompts/tailwindcss.md in the studio repo.
Every finding above also carries its own citation.