whats-new-sonnet-5-5 changedmodels/sonnet-5-5/whats-new-sonnet-5-5
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1010* [Forced tool use returns an error](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#forced-tool-use-is-not-supported).
1111* [Thinking blocks are tied to the model and the conversation](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#thinking-blocks-are-tied-to-the-model-that-produced-them).
1212* [On the Claude API and Google Cloud, the earlier `computer_20251124` computer use tool is not accepted](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#computer-20251124-is-not-supported).
13* [The advisor tool rejects Claude Opus 4.8, Claude Opus 4.7, and Claude Sonnet 5 as advisors](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#advisor-tool-pairings).
13* [The advisor tool rejects Claude Opus 4.8, Claude Opus 4.7, Claude Sonnet 5, and Claude Haiku 5.5 as advisors](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#advisor-tool-pairings).
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1515One more change alters the response shape without failing any request: [text between tool calls comes back in `thinking` blocks](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#text-between-tool-calls). An application that streams that text to its users goes quiet between tool calls until it sets a `display` value that returns the text, or turns off up-front thinking with `between_tools`.
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4848
4949### Thinking blocks are tied to the model and the conversation
5050
51Every thinking block records which model produced it. Each model reads its own blocks and only some other models' blocks. Claude Sonnet 5.5 reads thinking blocks from Claude Sonnet 5, Claude Opus 4.8, Claude Haiku 4.5, and earlier models, but not from Claude Opus 5, Claude Opus 5.5, or any Claude Fable or Claude Mythos model. On the Claude API and Google Cloud, Claude Opus 5.5 reads Claude Sonnet 5.5 thinking blocks; no other model does.
51Every thinking block records which model produced it. Each model reads its own blocks and only some other models' blocks. Claude Sonnet 5.5 reads thinking blocks from Claude Sonnet 5, Claude Opus 4.8, Claude Haiku 4.5, and earlier models, and, on the Claude API and Google Cloud, from Claude Haiku 5.5, but not from Claude Opus 5, Claude Opus 5.5, or any Claude Fable or Claude Mythos model. On the Claude API and Google Cloud, Claude Opus 5.5 reads Claude Sonnet 5.5 thinking blocks; no other model does.
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5353So a conversation that moves from Claude Sonnet 5 onto Claude Sonnet 5.5, or from Claude Sonnet 5.5 up to Claude Opus 5.5 on the Claude API and Google Cloud, keeps its reasoning, and any other move away from Claude Sonnet 5.5 runs the turns after the switch without it. When a request carries a block the target model can't read, the API drops it before the model sees it: the request succeeds, and dropped blocks aren't billed. With the `thinking-binding-controls-2026-08-01` beta header, the drop is reported in a top-level `input_transformations` array. See [Switching models mid-conversation](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#switching-models).
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7171### Some advisor tool pairings are not supported
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73With the [advisor tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool) (beta), a Claude Sonnet 5.5 executor needs Claude Mythos 5.1, Claude Fable 5.1, Claude Mythos 5, Claude Fable 5, Claude Opus 5.5, or Claude Opus 5 as its advisor, or Claude Sonnet 5.5 itself. Claude Opus 4.8, Claude Opus 4.7, and Claude Sonnet 5 advisors work with a Claude Sonnet 5 executor, but with a Claude Sonnet 5.5 executor they return a 400 `invalid_request_error`. Every advisor that Claude Sonnet 5.5 accepts returns its advice encrypted, as an `advisor_redacted_result` block, so your client can't read the advice text. See the advisor tool's [Model compatibility](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#model-compatibility) and [Result variants](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#result-variants).
73With the [advisor tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool) (beta), a Claude Sonnet 5.5 executor needs Claude Mythos 5.1, Claude Fable 5.1, Claude Mythos 5, Claude Fable 5, Claude Opus 5.5, or Claude Opus 5 as its advisor, or Claude Sonnet 5.5 itself. Claude Opus 4.8, Claude Opus 4.7, Claude Sonnet 5, and Claude Haiku 5.5 advisors work with a Claude Sonnet 5 executor, but with a Claude Sonnet 5.5 executor they return a 400 `invalid_request_error`. Every advisor that Claude Sonnet 5.5 accepts returns its advice encrypted, as an `advisor_redacted_result` block, so your client can't read the advice text. See the advisor tool's [Model compatibility](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#model-compatibility) and [Result variants](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#result-variants).
7474
7575## Feature support
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1601602. Replace `tool_choice` types `any` and `tool` with `auto` plus [strict tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/strict-tool-use).
1611613. Keep conversations append-only. A request that replays a Claude Sonnet 5.5 thinking block after an edit to earlier history can return a 400 error. See [Thinking blocks are tied to the model and the conversation](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#thinking-blocks-are-tied-to-the-model-that-produced-them).
1621624. If you use computer use through `computer_20251124` on the Claude API or Google Cloud, [move to the toolset](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124).
1635. If you use the advisor tool with a Claude Opus 4.8, Claude Opus 4.7, or Claude Sonnet 5 advisor, [switch to an advisor that Claude Sonnet 5.5 accepts](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#advisor-tool-pairings).
1635. If you use the advisor tool with a Claude Opus 4.8, Claude Opus 4.7, Claude Sonnet 5, or Claude Haiku 5.5 advisor, [switch to an advisor that Claude Sonnet 5.5 accepts](https://platform.claude.com/docs/en/models/sonnet-5-5/whats-new-sonnet-5-5#advisor-tool-pairings).
1641646. If your interface shows the text between tool calls, set `thinking.display` when you use adaptive thinking. With `between_tools`, the text comes back without it. See [Text between tool calls is returned in thinking blocks](https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide#text-between-tool-calls).
165165
166166The [migration guide](https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide) has step-by-step instructions from Claude Sonnet 5 and earlier models, and the full checklist.
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