errors changedapi/errors
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505505messages.N: output_config.effort 'low' differs from the 'high' in effect before it; effort cannot change when thinking is disabled on this model. Use effort 'high', or enable thinking.
506506```
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508Claude 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 above.
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508510In 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.
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510512Sending `thinking: {"type": "between_tools"}` to any model other than Claude Sonnet 5.5 returns a 400 `invalid_request_error`:
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530532### Computer use tool version not supported
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532On the Claude API and Google Cloud, Claude Opus 5.5 and Claude Sonnet 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 either model 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` 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:
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534536```text wrap
535537'claude-opus-5-5' does not support tool types: computer_20251124.
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540542### Thinking block no longer matches the conversation
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542On Claude Fable 5.1, Claude Opus 5.5, and Claude Sonnet 5.5, the API accepts a replayed thinking block only while the `system` prompt, `tools`, and messages that preceded it are unchanged. For new accounts created on or after August 31, 2026, and for any request that sets `thinking.block_binding.prefix_mismatch_behavior` to `"error"`, a replayed block whose earlier history changed is rejected with a 400 `invalid_request_error` (with `"drop_block"`, the API drops the block and the request succeeds). The message starts with the position of the first failing block:
544On Claude Fable 5.1, Claude Opus 5.5, Claude Sonnet 5.5, and Claude Haiku 5.5, the API accepts a replayed thinking block only while the `system` prompt, `tools`, and messages that preceded it are unchanged. For new accounts created on or after August 31, 2026, and for any request that sets `thinking.block_binding.prefix_mismatch_behavior` to `"error"`, a replayed block whose earlier history changed is rejected with a 400 `invalid_request_error` (with `"drop_block"`, the API drops the block and the request succeeds). The message starts with the position of the first failing block:
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544546```text wrap
545547messages.{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".
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