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Sweep 06 Nov 2026 · 01:32Z Build v2.1.319 537 read Stable v2.1.311 Latest v2.1.319 Next v2.1.319 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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thinking-troubleshooting changedbuild-with-claude/thinking-troubleshooting

Nearest release: v2.1.315, published under an hour 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.

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First seen 14 Aug 2026 this site's first read of the page
Recorded edits16to this page, all time

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1818 
1919The table lists what each model supports, what it defaults to, and which `thinking.type` values it rejects with a 400 error; any value not listed as rejected is accepted. Only Claude Sonnet 5.5 accepts `"between_tools"`, and it takes that value in place of `"disabled"`.
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21| Model | Thinking types | Default | Rejected with 400 |
22| --------------------- | -------------------------------- | --------- | -------------------------- |
23| Claude Fable 5.1 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
24| Claude Mythos 5.1 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
25| Claude Fable 5 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
26| Claude Mythos 5 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
27| Claude Mythos Preview | Adaptive, extended | Always on | `"disabled"` |
28| Claude Opus 5.5 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
29| Claude Opus 5 | Adaptive only | On | `"enabled"`, `"disabled"`2 |
30| Claude Opus 4.8 | Adaptive only | Off | `"enabled"` |
31| Claude Opus 4.7 | Adaptive only | Off | `"enabled"` |
32| Claude Sonnet 5.5 | Adaptive, `between_tools`3 | On | `"enabled"`, `"disabled"` |
33| Claude Sonnet 5 | Adaptive only | On | `"enabled"` |
34| Claude Haiku 5.5 | Adaptive only | On | `"enabled"`, `"disabled"`2 |
35| Claude Opus 4.6 | Adaptive, extended (deprecated)1 | Off | None |
36| Claude Sonnet 4.6 | Adaptive, extended (deprecated)1 | Off | None |
37| Claude Opus 4.5 | Extended only | Off | `"adaptive"` |
38| Claude Haiku 4.5 | Extended only | Off | `"adaptive"` |
39| Claude Sonnet 4.5 | Extended only | Off | `"adaptive"` |
21| Model | Thinking types | Default | Rejected with 400 |
22| --------------------- | ------------------------------------------- | --------- | ------------------------------------- |
23| Claude Fable 5.1 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
24| Claude Mythos 5.1 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
25| Claude Fable 5 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
26| Claude Mythos 5 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
27| Claude Mythos Preview | Adaptive, extended | Always on | `"disabled"` |
28| Claude Opus 5.5 | Adaptive only | Always on | `"enabled"`, `"disabled"` |
29| Claude Opus 5 | Adaptive only | On | `"enabled"`, `"disabled"`<sup>2</sup> |
30| Claude Opus 4.8 | Adaptive only | Off | `"enabled"` |
31| Claude Opus 4.7 | Adaptive only | Off | `"enabled"` |
32| Claude Sonnet 5.5 | Adaptive, `between_tools`<sup>3</sup> | On | `"enabled"`, `"disabled"` |
33| Claude Sonnet 5 | Adaptive only | On | `"enabled"` |
34| Claude Haiku 5.5 | Adaptive only | On | `"enabled"`, `"disabled"`<sup>2</sup> |
35| Claude Opus 4.6 | Adaptive, extended (deprecated)<sup>1</sup> | Off | None |
36| Claude Sonnet 4.6 | Adaptive, extended (deprecated)<sup>1</sup> | Off | None |
37| Claude Opus 4.5 | Extended only | Off | `"adaptive"` |
38| Claude Haiku 4.5 | Extended only | Off | `"adaptive"` |
39| Claude Sonnet 4.5 | Extended only | Off | `"adaptive"` |
4040 
41*1 `enabled` and `budget_tokens` still work on these models but are deprecated; use adaptive thinking instead.*\
42*2 Claude Opus 5 and Claude Haiku 5.5 accept `"disabled"` at [effort](https://platform.claude.com/docs/en/build-with-claude/effort) `high` or below; combining it with effort `xhigh` or `max` returns a 400 error. On Claude Opus 5, this restriction is enforced on each request. On Claude Haiku 5.5, a per-message effort that differs from the level in effect also returns a 400 error.*\
43*3 Claude Sonnet 5.5 accepts `"between_tools"` at effort `high` or below. Combining it with effort `xhigh` or `max` returns a 400 error, and so does a per-message effort that differs from the level in effect.*
41*<sup>1</sup> `enabled` and `budget_tokens` still work on these models but are deprecated; use adaptive thinking instead.*\
42*<sup>2</sup> Claude Opus 5 and Claude Haiku 5.5 accept `"disabled"` at [effort](https://platform.claude.com/docs/en/build-with-claude/effort) `high` or below; combining it with effort `xhigh` or `max` returns a 400 error. On Claude Opus 5, this restriction is enforced on each request. On Claude Haiku 5.5, a per-message effort that differs from the level in effect also returns a 400 error.*\
43*<sup>3</sup> Claude Sonnet 5.5 accepts `"between_tools"` at effort `high` or below. Combining it with effort `xhigh` or `max` returns a 400 error, and so does a per-message effort that differs from the level in effect.*
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4545Models marked `Always on` cannot turn thinking off. Models marked `On` default to thinking. Claude Opus 5, Claude Sonnet 5, and Claude Haiku 5.5 accept `thinking: {type: "disabled"}`. On Claude Sonnet 5.5, send `thinking: {type: "between_tools"}` to turn off up-front thinking.
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