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Sweep 09 Oct 2026 · 17:27Z Build v2.1.296 517 read Stable v2.1.287 Latest v2.1.296 Next v2.1.296 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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507507 
508508Claude Haiku 5.5 accepts `thinking: {"type": "disabled"}` and holds it to the same two effort limits that apply to `between_tools`: at `xhigh` or `max` effort, or with a per-message `output_config.effort` that differs from the level in effect, the request returns a 400 `invalid_request_error` with the matching message shown earlier.
509509 
510In both messages, "enable thinking" means adaptive thinking: omit the `thinking` field or send `thinking: {"type": "adaptive"}`. Claude Sonnet 5.5 rejects `"enabled"` with a 400 error. To vary effort per turn, use adaptive thinking.
510In both messages, "enable thinking" means adaptive thinking: omit the `thinking` field or send `thinking: {"type": "adaptive"}`. Claude Sonnet 5.5 and Claude Haiku 5.5 reject `"enabled"` with a 400 error. To vary effort per turn, use adaptive thinking.
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512512Sending `thinking: {"type": "between_tools"}` to any model other than Claude Sonnet 5.5 returns a 400 `invalid_request_error`:
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532532### Computer use tool version not supported
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534On the Claude API and Google Cloud, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5 support [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) only as the `computer_toolset_20260801` toolset. On those platforms, sending any of these models a `tools` entry of the earlier `computer_20251124` type (with that tool's beta header) returns a 400 `invalid_request_error`. The message names the rejected type, then lists the tool types the model does accept after `Did you mean one of`. For Claude Opus 5.5, it begins:
534On the Claude API and Google Cloud, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5 support [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) only as the `computer_toolset_20260801` toolset. On those platforms, sending any of these models a `tools` entry of the earlier `computer_20251124` or `computer_20250124` type, with that tool's beta header, returns a 400 `invalid_request_error`. The message names the rejected type, then lists the tool types the model does accept after `Did you mean one of`. For Claude Opus 5.5, it begins:
535535 
536536```text wrap
537537'claude-opus-5-5' does not support tool types: computer_20251124.
538538```
539539 
540The API returns the same message for any Anthropic-defined tool type that the requested model doesn't support. Declare `{"type": "computer_toolset_20260801"}` without the beta header and update your agent loop as described in [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). Earlier models that support the toolset keep accepting `computer_20251124`, as do Claude Opus 5.5 and Claude Sonnet 5.5 on Amazon Bedrock.
540The API returns the same message for any Anthropic-defined tool type that the requested model doesn't support. Declare `{"type": "computer_toolset_20260801"}` without the beta header and update your agent loop as described in [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). To move from `computer_20250124`, see [Move computer use to the toolset](https://platform.claude.com/docs/en/models/haiku-5-5/migration-guide#computer-use-toolset) in the Claude Haiku 5.5 migration guide. Earlier models that support the toolset keep accepting `computer_20251124`, as do Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5 on Amazon Bedrock.
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542542### Thinking block no longer matches the conversation
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547547messages.{i}.content.{j}: Invalid `signature` in `thinking` block. The block is bound to a different conversation. Remove the block, or set `thinking.block_binding.prefix_mismatch_behavior` to "drop_block".
548548```
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550Without the `thinking-binding-controls-2026-08-01` beta header the message also names that header. Keep the conversation history append-only, or send the beta header with `prefix_mismatch_behavior: "drop_block"` to drop the block and continue. On Claude Sonnet 5.5, `block_binding` works only with `thinking: {"type": "adaptive"}`. With `between_tools`, keep the history append-only, or strip the thinking blocks from the edited turn on. A block from a model the target model can't read is dropped rather than rejected. See [Keeping the prefix unchanged](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#prefix-check) and [Troubleshooting thinking](https://platform.claude.com/docs/en/build-with-claude/thinking-troubleshooting#error-thinking-block-signature).
550Without the `thinking-binding-controls-2026-08-01` beta header the message also names that header. Keep the conversation history append-only, or send the beta header with `prefix_mismatch_behavior: "drop_block"` to drop the block and continue. On Claude Sonnet 5.5 and Claude Haiku 5.5, `block_binding` works only with `thinking: {"type": "adaptive"}`. With `between_tools` on Claude Sonnet 5.5, or `thinking: {"type": "disabled"}` on Claude Haiku 5.5, keep the history append-only, or strip the thinking blocks from the edited turn on. A block from a model the target model can't read is dropped rather than rejected. See [Keeping the prefix unchanged](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking#prefix-check) and [Troubleshooting thinking](https://platform.claude.com/docs/en/build-with-claude/thinking-troubleshooting#error-thinking-block-signature).
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552552Sending `thinking.block_binding` without the `thinking-binding-controls-2026-08-01` [beta header](https://platform.claude.com/docs/en/api/beta-headers) returns a 400 `invalid_request_error` whose message ends in:
553553 
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