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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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whats-new-opus-5-5 changedmodels/opus-5-5/whats-new-opus-5-5

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8181* **The default effort is `medium`.** A request that omits `effort` runs at `medium`; on Claude Opus 5 it ran at `high`. Set `effort` explicitly and re-run your sweep; see [Calibrate effort](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#calibrate-effort).
8282* **More thinking per turn at a given effort level.** At the same [effort](https://platform.claude.com/docs/en/build-with-claude/effort) setting the model tends to think more per turn than Claude Opus 5, most of all at `xhigh` and `max`. Re-run your effort sweep rather than carrying a setting over, and leave room in `max_tokens` for the thinking. See [Calibrate effort](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#calibrate-effort).
83* **Text between tool calls comes back in thinking blocks.** The short notes the model writes between tool calls arrive as [progress-update `thinking` blocks](https://platform.claude.com/docs/en/build-with-claude/thinking#progress-updates) rather than `text` blocks, so at the default `display: "omitted"` an application that streams them to its users goes quiet between tool calls, with no error. The [migration guide](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#text-between-tool-calls) has the fix for receiving them, and [User-facing progress updates](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#user-facing-progress-updates) covers how to ask for more of them.
84* **More safeguard categories.** The model runs a biology safety classifier in addition to the cybersecurity one. As on Claude Opus 5, requests that push it to reproduce its internal reasoning in the response text might be declined with the `reasoning_extraction` category. See [Refusals and fallback](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#refusals-and-fallback) and [Safeguard refusals](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#safeguard-refusals).
83* **Text between tool calls comes back in thinking blocks.** The short notes the model writes between tool calls arrive as [progress-update `thinking` blocks](https://platform.claude.com/docs/en/build-with-claude/thinking#progress-updates) rather than `text` blocks, so at the default `display: "omitted"` an application that streams them to its users goes quiet between tool calls, with no error. The migration guide explains [how to receive text between tool calls](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#text-between-tool-calls), and [User-facing progress updates](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#user-facing-progress-updates) covers how to ask for more of them.
84* **More safeguard categories.** The model runs a biology safety classifier in addition to the cybersecurity one. As on Claude Opus 5, requests that push it to reproduce its internal reasoning in the response text might be declined with the `reasoning_extraction` category. See [Refusals and fallback in Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#refusals-and-fallback) and [Safeguard refusals](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#safeguard-refusals).
8585* **Sharper reading of charts, diagrams, and screenshots.** The model reads values off dense charts and layout-dependent visuals much more precisely without tools, so prompt-side vision workarounds built for earlier models might no longer be needed; image tools still add accuracy on the densest inputs. See [Tools for complex visual inputs](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#tools-for-complex-visual-inputs).
8686 
8787If your Claude Opus 5 integration ran with thinking disabled, see [Prompts written for thinking disabled](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#prompts-written-for-thinking-disabled) alongside the breaking change [Thinking can't be disabled](https://platform.claude.com/docs/en/models/opus-5-5/whats-new-opus-5-5#thinking-cant-be-disabled). For the capability gains in agentic coding and code review, knowledge work, communication, visual inputs, and computer use, see [Capabilities relevant to prompting](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-opus-5-5#capability-improvements).
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