whats-new-opus-5-5 changedmodels/opus-5-5/whats-new-opus-5-5
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### Some computer use tool versions are not supported ### The `computer_20251124` computer use tool is not supported on the Claude API and Claude Models on Google Cloud (Google managed)
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44description: Overview of breaking changes, feature support, and behavior differences in Claude Opus 5.5.
55---
66
7Claude Opus 5.5 is built for long-running agentic coding and knowledge work, priced at $4 / $20 USD per million input / output tokens. Four breaking changes affect code already running on Claude Opus 5: [thinking can’t be disabled](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#thinking-cant-be-disabled), [forced tool use returns an error](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#forced-tool-use-is-not-supported), [thinking blocks are tied to the model and the conversation](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#thinking-blocks-are-tied-to-the-model-that-produced-them), and, on the Claude API and Claude Models on Google Cloud (Google managed), [the earlier `computer_20251124` computer use tool is not accepted](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#computer-20251124-is-not-supported). The first three also apply on Claude Fable 5.1. A further 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/opus-5-5/whats-new-opus-5-5#text-between-tool-calls) whose text is empty at the default `display` setting. An application that streams that text to its users as progress updates goes quiet between tool calls until it sets a `display` value that returns the text.
7Claude Opus 5.5 is built for long-running agentic coding and knowledge work, priced at $4 / $20 USD per million input / output tokens. Four breaking changes can affect code already running on Claude Opus 5:
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9* [Thinking can’t be disabled](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#thinking-cant-be-disabled).
10* [Forced tool use returns an error](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#forced-tool-use-is-not-supported).
11* [Thinking blocks are tied to the model and the conversation](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#thinking-blocks-are-tied-to-the-model-that-produced-them).
12* [Some computer use tool versions are not supported](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#computer-20251124-is-not-supported).
13
14The first three also apply on Claude Fable 5.1. A further 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/opus-5-5/whats-new-opus-5-5#text-between-tool-calls) whose text is empty at the default `display` setting. An application that streams that text to its users as progress updates goes quiet between tool calls until it sets a `display` value that returns the text.
15
916## New model
1017
1118| Model | Claude API ID | Description |
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4956The API also checks whether anything before a Claude Opus 5.5 thinking block (the `system` prompt, the `tools`, or an earlier message) has changed since the block was produced. Keep the conversation append-only: change instructions or tools with [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages) rather than edits. A request that replays a block after such a change and leaves `thinking.block_binding.prefix_mismatch_behavior` unset gets a 400 error on accounts created on or after August 31, 2026, 00:00 UTC. This applies on the Claude API and on cloud platforms. On accounts created before that date, the request gets the error only when it sets the field to `"error"`. To drop the affected blocks instead, send the `thinking-binding-controls-2026-08-01` beta header and set the field to `"drop_block"`. See [Preserved thinking](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking) and the migration guide’s [note on thinking blocks](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#thinking-blocks).
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51### The `computer_20251124` computer use tool is not supported on the Claude API and Claude Models on Google Cloud (Google managed)
58### Some computer use tool versions are not supported
5259
53Claude Opus 5 accepts [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) both as the `computer_toolset_20260801` toolset and, with the `computer-use-2025-11-24` beta header, as the earlier `computer_20251124` tool. On the Claude API and Claude Models on Google Cloud (Google managed), Claude Opus 5.5 supports only the toolset: a request that declares a `computer_20251124` tool returns a 400 `invalid_request_error`. The message names the rejected type, then lists the tool types the model does accept (`computer_toolset_20260801` among them) after `Did you mean one of`; it begins:
60Claude Opus 5.5 supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) through the `computer_toolset_20260801` toolset. On Amazon Bedrock, Claude Opus 5.5 also accepts the `computer_20251124` tool with the `computer-use-2025-11-24` beta header. Claude Opus 5.5 returns a 400 error for any computer use tool version it doesn’t accept, such as `computer_20251124` on the Claude API. The Claude API’s `invalid_request_error` message names the rejected type and, after `Did you mean one of`, lists the tool types the model accepts. The message begins:
5461
5562```text wrap
5663'claude-opus-5-5' does not support tool types: computer_20251124.
5764```
5865
59To move an existing integration on the Claude API or Claude Models on Google Cloud (Google managed), follow [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124): drop the beta header, replace the `tools` entry with `{"type": "computer_toolset_20260801"}`, and update your agent loop for member `tool_use` blocks, batch actions, and `toolset_name` on results. On Amazon Bedrock, the earlier `computer_20251124` tool continues to work on Claude Opus 5.5 as it does on Claude Opus 5, so no change is needed there. For other platforms, see the computer use tool’s [API support](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#availability-feature-support) section. Integrations that already use the toolset, and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool), need no change. The migration guide shows the request [before and after](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
66Integrations that use the toolset need no change. To move a `computer_20251124` integration to the toolset, follow [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). Drop the beta header and replace the `tools` entry with `{"type": "computer_toolset_20260801"}`. Then update your agent loop for member `tool_use` blocks, batch actions, and `toolset_name` on results. The migration guide shows the request [before and after](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
6067
6168## Feature support
6269
63Claude Opus 5.5 supports [per-message effort](https://platform.claude.com/docs/en/build-with-claude/effort#change-effort-mid-conversation-beta) (beta), [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages), [task budgets](https://platform.claude.com/docs/en/build-with-claude/task-budgets), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) with a 512-token minimum cacheable prompt, [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview). On the Claude API and Claude Models on Google Cloud (Google managed), computer use requires the `computer_toolset_20260801` toolset (see the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#computer-20251124-is-not-supported)). See each feature’s page for model availability.
70Claude Opus 5.5 supports [per-message effort](https://platform.claude.com/docs/en/build-with-claude/effort#change-effort-mid-conversation-beta) (beta), [mid-conversation system messages](https://platform.claude.com/docs/en/build-with-claude/mid-conversation-system-messages), [task budgets](https://platform.claude.com/docs/en/build-with-claude/task-budgets), [prompt caching](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) with a 512-token minimum cacheable prompt, [batch processing](https://platform.claude.com/docs/en/build-with-claude/batch-processing), the [Files API](https://platform.claude.com/docs/en/build-with-claude/files), [PDF support](https://platform.claude.com/docs/en/build-with-claude/pdf-support), [vision](https://platform.claude.com/docs/en/build-with-claude/vision), and server-side and client-side [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview). See each feature’s page for model availability.
6471
6572### Fast mode
6673
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144151 ```
145152</CodeGroup>
146153
147Then remove any `thinking: {"type": "disabled"}` or `thinking: {"type": "enabled", ...}` settings and choose an [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level instead. 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). If you use computer use through `computer_20251124` on the Claude API or Claude Models on Google Cloud (Google managed), [move to the toolset](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). If your interface shows the text between tool calls, also set `thinking.display`; see [Text between tool calls is returned in thinking blocks](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#text-between-tool-calls). See the [migration guide](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide) for step-by-step instructions from Claude Opus 5 and earlier models, and the full checklist.
154Then remove any `thinking: {"type": "disabled"}` or `thinking: {"type": "enabled", ...}` settings and choose an [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level instead. 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). If you use computer use through `computer_20251124`, [move to the toolset](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). On Amazon Bedrock, `computer_20251124` also works. If your interface shows the text between tool calls, also set `thinking.display`; see [Text between tool calls is returned in thinking blocks](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#text-between-tool-calls). See the [migration guide](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide) for step-by-step instructions from Claude Opus 5 and earlier models, and the full checklist.
148155
149156## Next steps
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