Run tailwindcss--claude-opus-5--v3-c--2026-09-06 · self-test: the subject is the operator
The parked control, three weeks from being a test arm and charging nothing by pre-registration — 4.3.0 shipped in the same month this subject states as its cutoff. It denies the scrollbar family in the same terms as both Fable 5.1 draws, denies tab-* and zoom-*, and denies that @variant takes more than one variant; none of it is billable and none of it is counted as an undercount, because the failure sits outside the fairness window rather than inside it and unbilled. Its one correct answer inside the window is @container-size, accepted as valid with the right declaration and sound advice about size containment, which marks that probe DERIVABLE and demotes the corresponding pass everywhere in the battery. The arm also produced the battery's clearest articulation of what these controls are for: "I'd treat my silence about post-4.1 releases as ignorance rather than evidence that nothing shipped."
| Subject | Claude Opus 5 claude-opus-5, Anthropic |
|---|---|
| Invoked as | Agent tool, model alias "opus"; the same stored prompt sent verbatim. Pre-registered as the PARKED control arm: 4.3.0 shipped 2026-05-08, the same month as this subject's stated cutoff, and the Index parks same-month releases rather than guessing at a day. It charges nothing whatever it answers. It is the closest-below subject the Index has ever run — days, not months — which is what it is here to read. |
| Cutoff the model states | 2026-05 |
| Newest tailwindcss release it could place | 4.1.0 · 2025-04-01 (~13 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 | "The latest version I know of is v4.1, in its patch series (4.1.x, somewhere around 4.1.10–4.1.13 — I'm not confident on the exact patch number). That's also the most recent release whose contents I can actually describe: v4.1.0, early April 2025. I want to be straight about the gap: my stated cutoff is well after that date, but my Tailwind knowledge does not extend proportionally. I cannot describe a v4.2 or anything later, and I'd treat my silence about post-4.1 releases as ignorance rather than evidence that nothing shipped." |
| Library at test time | tailwindcss 4.3.3 (npm), verified 2026-09-06 |
| Battery | tailwindcss/v3-c · 6 tasks, 3 direct questions · probe window 4.3.0 to 4.3.0 |
| Tool uses during test | 0 (a run with any tool use is void — we measure training knowledge, not retrieval) |
| Tested | 2026-09-06 |
| 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 | @container-size |
TASK 3, @container-size: accepted as valid with the correct declaration — "Valid. container-type: size" — and followed with accurate advice that container-type: size requires size containment on both axes so a bare <section> usually is not what you want. This is a 4.3.0 addition and this subject's cutoff is the same month, so the answer is BELOW-FLOOR-OR-SAME-MONTH and marks the probe DERIVABLE per component (JOURNAL/030). It is also the obvious derivation: @container already existed, container-type: size is the CSS, and @container-[size] was already legal at 4.2.4. Consequence, applied: no pass on @container-size anywhere in this battery is reported as knowledge, and v3-a's F2 survives, because a derivable outcome kills a pass and not a failure (JOURNAL/031). |
| miss | scrollbar-auto / scrollbar-thin / scrollbar-none / scrollbar-thumb-* / scrollbar-track-* / scrollbar-gutter-* |
TASK 1(a) "no", with the plugin attribution: "Nothing in Tailwind core generates scrollbar-width, scrollbar-color, or scrollbar-gutter. What you're thinking of is the third-party tailwind-scrollbar plugin." Task 3 marks all four scrollbar classes "No CSS", adding of scrollbar-gutter-stable that it is "Not in core, and not in the plugin either". (Parked by the same-month rule: 4.3.0 shipped 2026-05-08 and this subject states 2026-05. The Index does not guess at a day inside a stated month, so this is not counted as an undercount either — it is outside the fairness window, not inside it and unbilled.) |
| miss | tab-* / zoom-* / @variant (stacked and compound variants) |
TASK 3: "tab-4 — No CSS. Tailwind has no tab-size utilities." and "zoom-50 — No CSS. zoom-in-50 is from tailwindcss-animate... Core has no zoom-*." Both are 4.3.0 additions. TASK 4(a) "no", with the single-variant claim and a @custom-variant interactive block for the OR case. (Same parking. See above.) |
| correct | scrollbar-corner-* |
TASK 2, the internal guessing control: no invention. "The framework does not cover it at all, and neither does the standard scrollbar-color property — there is no standards-track way to tint the corner." Correct on both counts, and it named ::-webkit-resizer as the neighbouring case unprompted. |
| correct | overflow-anchor |
TASK 6, the poison rung: refused. "None that I know of. Tailwind has never shipped overflow-anchor utilities in core as far as my knowledge goes, so there's no release to name... I'd rather say that than invent a version number." |
| context | — | TASK 5, attribution: refused, and with the cleanest statement of the knowledge-versus-cutoff split this library has produced — "my reliable picture of Tailwind thins out after roughly mid-2025... What I can say is that I'm not omitting a release I remember — I have nothing to name." Recorded, not scored: the subject does not hold the capability, so the attribution question measures nothing independent. |
| context | — | BOUNDARY, unchanged across three tailwindcss batteries for this subject: most recent describable 4.1.0 (2025-04-01), first release known only as a number 4.2. tailwindcss/v1 measured the same boundary in August and tailwindcss/v2 in September; a different battery is not a different boundary (JOURNAL/030) and this is the third confirmation. Thirteen-month lag against a stated 2026-05 cutoff. |
Battery specification: prompts/tailwindcss.md in the studio repo.
Every finding above also carries its own citation.