migration-guide changedmodels/opus-5-5/migration-guide

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118511851. **Consider task budgets (beta):** For agentic workloads, [task budgets](https://platform.claude.com/docs/en/build-with-claude/task-budgets) tell the model how many tokens it has for a full agentic loop. They require the `task-budgets-2026-03-13` beta header.

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11872. **Consider mid-conversation tool changes (beta):** Mid-conversation tool changes (beta header `mid-conversation-tool-changes-2026-07-01`) are available on the Claude API, Amazon Bedrock, and Google Cloud. They let you add or remove tools between turns of a conversation without invalidating [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) hits on earlier turns. Without the header, a changed tool list invalidates the cached prefix.

11872. **Consider mid-conversation tool changes (beta):** Mid-conversation tool changes let you add or remove tools between turns of a conversation without invalidating [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) hits on earlier turns. Changing the `tools` array itself invalidates the cached prefix. On the Claude API, send the `inline-tools-2026-09-15` beta header. The older `mid-conversation-tool-changes-2026-07-01` header still works for changes that name a tool by reference, on the Claude API, Amazon Bedrock, and Google Cloud.

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11891189## Migrating to Claude Opus 5.5 from Claude Opus 4.7

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155515554. **Remove interleaved thinking beta header:** With adaptive thinking, interleaved thinking is automatic on every model that supports adaptive thinking. Remove `betas=["interleaved-thinking-2025-05-14"]` from your requests.

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15575. **Migrate to output\_config.format:** If using structured outputs, update `output_format={...}` to `output_config={"format": {...}}`. The API still accepts the deprecated `output_format` parameter, but it will be removed in a future model release. The Python SDK (v1.0 and later) does not accept `output_format={...}` on `client.beta.messages.create()` or `count_tokens()`. The `output_format=Model` argument of the `parse()` and `stream()` helpers is unchanged.

15575. **Migrate to output\_config.format:** If using structured outputs, update `output_format={...}` to `output_config={"format": {...}}`. The `output_format` parameter is deprecated and will be removed in the future. To use it anyway, add the `structured-outputs-2025-11-13` beta header. Without it, the API returns a 400 error. The Python SDK (v1.0 and later) does not accept `output_format={...}` on `client.beta.messages.create()` or `count_tokens()`. The `output_format=Model` argument of the `parse()` and `stream()` helpers is unchanged.

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15591559### Migrating from Claude 4.1 or earlier

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