migration-guide changedmodels/opus-5-5/migration-guide
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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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2828* **Tool choice:** Use `tool_choice` `{"type": "auto"}` (the default) or `{"type": "none"}`. Forcing a tool call with `{"type": "any"}` or `{"type": "tool", "name": "..."}` is rejected. See the [before and after for tool choice](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#forced-tool-use).
2929* **Sampling parameters:** Omit `temperature`, `top_p`, and `top_k`. Use prompting to guide the model’s behavior.
3030* **Prefill:** Don’t end `messages` with a prefilled assistant turn: it is rejected. Use [structured outputs](https://platform.claude.com/docs/en/build-with-claude/structured-outputs) or system prompt instructions instead.
31* **Computer use:** On the Claude API and Claude Models on Google Cloud (Google managed), declare computer use as the `computer_toolset_20260801` toolset; the earlier `computer_20251124` tool is rejected there. See the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
31* **Computer use:** Declare computer use as the `computer_toolset_20260801` toolset. On Amazon Bedrock, `computer_20251124` also works. See the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
3232* **Context window:** No context-window beta header is needed. The [1M token context window](https://platform.claude.com/docs/en/build-with-claude/context-windows) is the default, and a header sent for older models has no effect.
3333
3434The following request satisfies every item in the list: effort is set, and there is no `thinking` field. Where the example prints text, it finds the text block by its type, because `thinking` blocks come first.
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279279* Remove `thinking: {"type": "disabled"}` and `thinking: {"type": "enabled", ...}`; choose an effort level instead.
280280* Set `effort` explicitly: the default is `medium`, where Claude Opus 5’s is `high`.
281281* Replace `tool_choice` types `any` and `tool` with `auto` plus strict tool use or structured outputs.
282* If you use computer use on the Claude API or Claude Models on Google Cloud (Google managed), declare `computer_toolset_20260801` (no beta header) instead of `computer_20251124` and update your agent loop for the toolset. On Amazon Bedrock, keep `computer_20251124`; check 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 for other platforms.
282* If you use an earlier computer use tool version, declare `computer_toolset_20260801` (no beta header) instead and update your agent loop for the toolset. On Amazon Bedrock, `computer_20251124` also works.
283283* If a router or fallback can move a conversation from Claude Opus 5.5 to another model, expect that model to run without Claude Opus 5.5’s thinking blocks (Claude Fable 5.1 and Claude Mythos 5.1 on the Claude API are the exception and keep them). Claude Opus 5.5 itself reads thinking from Claude Opus 5, from earlier Opus, Sonnet, and Haiku models, and, on the Claude API and Claude Models on Google Cloud (Google managed), from Claude Sonnet 5.5 and Claude Haiku 5.5, but not from Claude Fable or Claude Mythos models.
284284* Read content blocks by `type`, and pass `thinking` blocks back unmodified in tool-use loops.
285285* If your interface renders text between tool calls, set `display: "updates"` (beta) or `"summarized"` and render the non-empty `thinking` blocks.
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879879On the Claude API, Claude Fable 5.1 and Claude Mythos 5.1 read Claude Opus 5.5 thinking blocks; no other model does. A router or fallback that moves a conversation from Claude Opus 5.5 to any other model runs those turns without them. In the other direction, Claude Opus 5.5 reads thinking blocks from Claude Opus 5, from earlier Opus, Sonnet, and Haiku models, and, on the Claude API and Claude Models on Google Cloud (Google managed), from Claude Sonnet 5.5 and Claude Haiku 5.5, but not from Claude Fable or Claude Mythos models. Keep the conversation append-only (no edits to the `system` prompt, `tools`, or earlier messages mid-conversation) so the blocks stay valid; Claude Code, claude.ai, Claude Managed Agents, and the Claude Agent SDK already do. On accounts created on or after August 31, 2026, 00:00 UTC, on the Claude API and on cloud platforms, a request that replays a thinking block after such an edit and leaves `thinking.block_binding.prefix_mismatch_behavior` unset gets a 400 error. There is no code change for append-only integrations. See [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 [Preserved thinking](https://platform.claude.com/docs/en/build-with-claude/preserved-thinking).
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881#### The `computer_20251124` computer use tool is not supported on the Claude API and Claude Models on Google Cloud (Google managed)
881#### Some computer use tool versions are not supported
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883On the Claude API and Claude Models on Google Cloud (Google managed), a `tools` entry of type `computer_20251124` returns a 400 error (`'claude-opus-5-5' does not support tool types: computer_20251124.`, followed by the tool types the model accepts). Declare the `computer_toolset_20260801` toolset instead: drop the beta header and send the entry with no `name` or display dimensions. In your agent loop, handle member `tool_use` blocks (the action is the block’s `name`, not `input.action`), several of them per turn, and echo `toolset_name` on every result. The request change is shown below; the agent-loop changes are listed in [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124). 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. See [The `computer_20251124` computer use tool is not supported on the Claude API and Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#computer-20251124-is-not-supported).
883Claude Opus 5.5 supports computer use 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. It doesn’t accept `computer_20250124` on any platform. On the Claude API, the error message begins `'claude-opus-5-5' does not support tool types: computer_20251124.` and then lists the tool types the model accepts.
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885Before. Claude Opus 5 accepts this request, and on the Claude API and Claude Models on Google Cloud (Google managed), Claude Opus 5.5 rejects it with a 400 error:
885Integrations that use the toolset need no change. To move a `computer_20251124` integration to the toolset, drop the beta header and send the `computer_toolset_20260801` entry with no `name` or display dimensions. In your agent loop, handle every member `tool_use` block in a turn and echo `toolset_name` on every result. Read the action from each block’s `name`, not from `input.action`. [Migrate from `computer_20251124`](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool#migrate-from-computer-20251124) lists the agent-loop changes.
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887Before. Claude Opus 5 accepts this request, and Claude Opus 5.5 rejects it with a 400 error on the Claude API:
888
887889<CodeGroup>
888890 ```bash cURL
889891 curl https://api.anthropic.com/v1/messages \
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119912015. **Fast mode:** Claude Opus 5.5 supports [fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) on the Claude API. Fast mode is not available on Claude Opus 4.7, where requests with `speed: "fast"` return an error. Set `speed: "fast"` on your requests. Claude Opus 5.5 doesn’t need a beta header.
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12016. **Computer use toolset and browser use tool:** On the Claude API and Claude Models on Google Cloud (Google managed), Claude Opus 5.5 supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages. Claude Opus 4.7 supports neither. On those platforms Claude Opus 5.5 doesn’t accept the earlier `computer_20251124` tool; see the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
12036. **Computer use toolset and browser use tool:** Claude Opus 5.5 supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages. Claude Opus 4.7 supports neither. To move a `computer_20251124` integration to the toolset, see the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
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12031205## Migrating to Claude Opus 5.5 from Claude Opus 4.6 and earlier Opus models
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16321634 * **Text editor:** Use `text_editor_20250728` and `str_replace_based_edit_tool`. See the [Text editor tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/text-editor-tool) documentation for details.
16331635 * **Code execution:** Upgrade to `code_execution_20260521`. See the [Code execution tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool#upgrade-to-latest-tool-version) documentation for migration instructions.
1634 * **Computer use:** On the Claude API and Claude Models on Google Cloud (Google managed), Claude Opus 5.5 accepts computer use only as the `computer_toolset_20260801` toolset: the earlier `computer_20250124` and `computer_20251124` tools are rejected there. See the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
1636 * **Computer use:** Use the `computer_toolset_20260801` toolset in place of `computer_20250124`, which Claude Opus 5.5 doesn’t accept. On Amazon Bedrock, `computer_20251124` also works. See the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
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163616383. **Handle the `refusal` stop reason**
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