Partly: in 3 runs, Claude Opus 5.5's better-auth attribution reaches 1.4.0 (2025-11-22), inside better-auth 1, and stops there — better-auth was at 1.7.6 when this index last tested it (2026-09-28). That is ~7 months below the training cutoff the subject stated in those runs (2026-06). 2 findings are currently charged against Claude Opus 5.5 on better-auth (1x S2 silently-wrong, 1x S3 deprecated), 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.
3 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 4 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 | Denies the email-OTP plugin has a resend-reuse option and hand-rolls one with a Redis cache inside an async generateOTP — a function the plugin types as synchronous, so the workaround fails the type checkemailOTP({ resendStrategy }) |
1.5.6 2026-03-22 |
yes | run · source |
| S3deprecated | Denies the two-factor client takes a page option and says the string option was replaced by the callback — right about 0.x → 1.0.0, unaware it came back at 1.5.6twoFactorClient({ twoFactorPage }) |
1.5.6 2026-03-22 |
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 prisma and 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 Opus 5.5 on the other libraries: