What
shared/model-migration.md gains a section for the new Opus covering the two behaviours that break existing request code.
Details
- Breaking change 1: thinking is on by default when
thinkingis omitted, a silent cost and truncation change measured againstmax_tokens. - Breaking change 2:
thinking: {type: "disabled"}is accepted only at efforthighor lower; pairing it withxhighormaxreturns 400, validated per request. - Documents disabled-thinking failure modes: tool calls emitted as plain text, and
<thinking>tag leakage. - Also notes a 512-token cache minimum, a separate rate-limit bucket, and adds a [BLOCKS]/[TUNE] checklist.
- Older Opus rows in the migration table now all target the new ID.
Evidence
### Breaking change 2: disabling thinking is capped at
Strings lifted out of the shipped bundle, so the claim above can be checked against them.