Partly: in 7 runs, Claude Fable 5's better-auth attribution reaches 1.3.0 (2025-07-19), inside better-auth 1, and stops there — better-auth was at 1.7.3 when this index last verified against it (2026-09-06). That is ~6 to ~18 months below the training cutoff the subject stated in those runs (2026-01). 2 findings are currently charged against Claude Fable 5 on better-auth (2x S2 silently-wrong), each reproduced in a published run and checked against better-auth's own release notes. Read the boundary precisely: it is the newest release whose contents the model can correctly attribute to that release, not the newest better-auth feature it can use. Past it a model often writes working code with a newer API while naming the wrong release for it.
Answer class inside, decided by one rule applied to every page
of this kind: every measured boundary is at or above the first release of the major named in the question. Every figure below is read from
the dataset at build time; nothing on this page is written by hand.
| Battery | Newest release it can place | Oldest it cannot | Lag vs stated cutoff |
|---|---|---|---|
| v1 2026-09-01 | 1.3.0 2025-07-19 |
1.4.0 2025-11-22 |
~6 months |
| v2-a 2026-09-02 | 1.3.0 2025-07-19 |
1.4.0 2025-11-22 |
~6 months |
| v2-b 2026-09-02 | 1.3.0 2025-07-19 |
1.4.0 2025-11-22 |
~6 months |
| v3-d 2026-09-03 | 1.3.0 2025-07-19 |
1.4.0 2025-11-22 |
~18 months |
| v4-e 2026-09-03 | 1.3.0 2025-07-19 |
1.4.0 2025-11-22 |
~18 months |
| v4-f 2026-09-03 | 1.3.0 2025-07-19 |
1.4.0 2025-11-22 |
~18 months |
| v5-d 2026-09-03 | 1.3.0 2025-07-19 |
1.4.0 |
~6 months |
6 measurements of this pair, all giving the same boundary. Of those, 2 came from the same stored prompt file, sent concurrently and blind: they agreed exactly.
better-auth published 3 minor or major releases in the twelve months before this model’s stated cutoff, which is the scale a spread should be read against.
“Chargeable” means the change was published before this model’s own stated cutoff, so it had the opportunity to know it.
| Severity | Belief | Changed in | Chargeable | Proof |
|---|---|---|---|---|
| S2silently-wrong | States that better-auth offers no stateless, store-free session mode, and names cookieCache, Redis and the jwt plugin as the only optionsstateless / database-less sessions |
1.4.0 2025-11-22 |
yes | run · source |
| S2silently-wrong | States that operating with no server-side session state is not what the library supports, which stopped being true in 1.4.0stateless session management |
1.4.0 2025-11-22 |
yes | run · source |
The better-auth correction pack states what is true now for each corrected fact, with a primary-source citation, as markdown you can paste into a rules file (raw). What a correction pack measurably changed when one was tested — a pre-registered run on zod — is on the benchmark page, including where it changed nothing.
All of them at once: Which Claude model knows better-auth 1 best?
Other subjects on better-auth:
Claude Fable 5 on the other libraries: