Auto-following to the newest Opus moved the failure rather than removing it.
The deploy's own smoke output showed it: 404 "model not found" became
HTTP 400: `temperature` is deprecated for this model.
Anthropic removed temperature/top_p/top_k on the current generation (Opus 5,
Sonnet 5, Opus 4.7/4.8, Fable 5), and the adapter sends temperature: 0
unconditionally. So the gate's prompt-selection was still degrading on every
call -- just with a different status code.
A list of which models accept sampling would rot exactly the way the pinned
model ids did, which is the whole thing this branch is trying to stop. So the
provider learns it instead: the first 400 naming a sampling parameter drops it
and retries, and remembers the model so every later call omits it up front.
One wasted call, once, rather than a hardcoded table to maintain.
The match is deliberately narrow -- a 400 must actually name temperature/top_p/
top_k. An unrelated 400 (missing max_tokens, bad schema) propagates untouched;
there is a test for that, because a broad match here would silently swallow
real request errors and retry them pointlessly.
Verified live: claude-opus-latest -> claude-opus-5, first attempt 400 on
temperature, retry succeeds past it. The retry then hit HTTP 429 -- the
personal OAuth token's rate limit, which is the pre-existing credential-tiering
issue, not this path.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GqMidYEGUJG5fxeoTELBu2
