migration-guide changedmodels/sonnet-5-5/migration-guide

Nearest release: v2.1.286, published 6 hours before this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Recorded here 30 Sep 2026 23:37 UTC

Lines+1added

Lines−1removed

From line 242 where the diff opens

First seen 29 Sep 2026 this site's first read of the page

Recorded edits2to this page, all time

The whole hunk

from line 242, old and new numbered

lines

from line 242

242242To turn off up-front thinking on Claude Sonnet 5.5, send `thinking: {"type": "between_tools"}`. It's the lowest thinking setting. Its progress updates between tool calls still come back as `thinking` blocks with their summary text. Without tools, the response contains only text. Claude Sonnet 5 turns thinking off with `thinking: {"type": "disabled"}` instead, and earlier models run without thinking by default. On Claude Sonnet 5.5, `disabled` returns a 400 `invalid_request_error`:

243243

244244```text wrap

245"thinking.type.disabled" is not supported for this model. Use "thinking.type.between_tools" for the lowest thinking setting, or "thinking.type.adaptive" and "output_config.effort" to control thinking behavior.

245To turn thinking off on this model, send "thinking": {"type": "between_tools"} instead of {"type": "disabled"}. The model does not think before responding. The short updates it writes between tool calls come back as thinking blocks.

246246```

247247

248248`between_tools` works on every platform that offers Claude Sonnet 5.5, with no beta header. It's accepted at `low`, `medium`, and `high` effort. At `xhigh` or `max`, it returns a 400 error. To run at those levels, use adaptive thinking: omit the `thinking` field or send `thinking: {"type": "adaptive"}`. `between_tools` takes no other field: `display`, `budget_tokens`, or `block_binding` sent with it returns a 400 error. With [server-side fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#server-side-fallback), a `between_tools` request that falls back to Claude Sonnet 5 runs there with `thinking: {"type": "disabled"}`.