12 current findings across 20 models, verified against tailwindcss release notes. Latest tailwindcss at last verification: 4.3.3.
| Model | Stated cutoff | Attribution stops at | Lag |
|---|---|---|---|
| Claude Fable 5 | 2026-01 | 4.1.0 · 2025-04-01 | ~9 months |
| Claude Fable 5 | 2026-01 | 4.1.0 · 2025-04-01 | ~9 months |
| Claude Fable 5.1 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Fable 5.1 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Fable 5.1 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Fable 5.1 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Haiku 4.5 | 2025-02 | 4.0.0 · 2025-01-21 | ~1 months |
| Claude Haiku 4.5 | 2025-02 | 4.0.0 · 2025-01-21 | ~1 months |
| Claude Opus 5 | 2026-05 | 4.1.0 · 2025-04-01 | ~13 months |
| Claude Opus 5 | 2026-05 | 4.1.0 · 2025-04-01 | ~13 months |
| Claude Opus 5 | 2026-05 | 4.1.0 · 2025-04-01 | ~13 months |
| Claude Opus 5 | 2026-05 | 4.1.0 · 2025-04-01 | ~13 months |
| Claude Opus 5.5 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Opus 5.5 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Opus 5.5 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Opus 5.5 | 2026-06 | 4.2.0 · 2026-02-18 | ~4 months |
| Claude Opus 5.5 | 2026-06 | 4.1.0 · 2025-04-01 | ~14 months |
| Claude Sonnet 5 | 2026-01 | 4.1.0 · 2025-04-01 | ~9 months |
| Claude Sonnet 5 | 2026-01 | 4.1.0 · 2025-04-01 | ~9 months |
| Claude Sonnet 5 | 2026-01 | 4.1.0 · 2025-04-01 | ~9 months |
Measured by asking each model what shipped in a given tailwindcss release, then checking the answer against the release timeline. Not inferred from the vendor’s cutoff date. This is the newest release the model can correctly place, not the newest tailwindcss feature it knows — a model past this point often uses a newer API correctly while naming the wrong release for it. Why that distinction matters.
The same data, split the way the question usually gets asked — one page per subject, with its boundary measurements, its findings on tailwindcss, and how repeatable the boundary was.
And the comparison, ranked by measured boundary and by nothing else: Which Claude model knows tailwindcss 4 best?
Sorted by severity. “Chargeable” means the change was published before that model’s own stated cutoff, so the model had the opportunity to know it.
| Severity | Belief | Model | Changed in | Chargeable | Proof |
|---|---|---|---|---|---|
| S2silently-wrong | Denies the 4.2.0 block-axis and logical-sizing utilities exist, and tells a colleague to rewrite working markup that uses themlogical property utilities |
Claude Fable 5.1 | 4.2.0 2026-02-18 |
yes | source |
| S2silently-wrong | Denies the 4.2.0 block-axis and logical-sizing utilities exist, and rejects working markup that uses themlogical property utilities |
Claude Opus 5 | 4.2.0 2026-02-18 |
yes | source |
| S2silently-wrong | Denies Tailwind ships scrollbar utilities, attributes the real class names to a third-party plugin, and rejects working markup that uses themscrollbar-auto / scrollbar-thin / scrollbar-none / scrollbar-thumb-* / scrollbar-track-* / scrollbar-gutter-* |
Claude Fable 5.1 | 4.3.0 2026-05-08 |
yes | source |
| S2silently-wrong | Rejects @container-size as not a core utility, in a review of markup where it compiles@container-size |
Claude Fable 5.1 | 4.3.0 2026-05-08 |
yes | source |
| S2silently-wrong | Denies a zoom-* family exists and attributes the name to an animation plugin, rejecting working markupzoom-* |
Claude Fable 5.1 | 4.3.0 2026-05-08 |
yes | source |
| S2silently-wrong | Denies Tailwind ships scrollbar utilities, says the class names belong to a plugin, and rejects working markup that uses themscrollbar-auto / scrollbar-thin / scrollbar-none / scrollbar-thumb-* / scrollbar-track-* / scrollbar-gutter-* |
Claude Opus 5.5 | 4.3.0 2026-05-08 |
yes | source |
| S2silently-wrong | Rejects zoom-50 and tab-4 as not core, in a review of markup where both compilezoom-* / tab-* |
Claude Opus 5.5 | 4.3.0 2026-05-08 |
yes | source |
| S3deprecated | States start-/end- are current and not deprecated, two releases after 4.2.0 deprecated themlogical inset utilities |
Claude Fable 5.1 | 4.2.0 2026-02-18 |
yes | source |
| S3deprecated | States start-/end- are current and explicitly not deprecated, two releases after 4.2.0 deprecated themlogical inset utilities |
Claude Opus 5 | 4.2.0 2026-02-18 |
yes | source |
| S3deprecated | Denies @variant accepts a stacked or comma-separated variant, and writes the block out three times for the OR case@variant (stacked and compound variants) |
Claude Fable 5.1 | 4.3.0 2026-05-08 |
yes | source |
| S3deprecated | Denies @variant accepts a stacked or comma-separated variant, nests the AND and writes the OR block out three times@variant (stacked and compound variants) |
Claude Opus 5.5 | 4.3.0 2026-05-08 |
yes | source |
| S4wrong-metadata | Version knowledge stops at 4.1.0, thirteen months before its stated cutoff | Claude Opus 5 | 4.2.0 2026-02-18 |
yes | source |