overview changedmodels/opus-5/overview
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1717## Overview
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19Claude Opus 5 is a step-change improvement over Claude Opus 4.8, with the largest gains in deep reasoning, agentic and long-horizon tasks, and test-time compute scaling. This page summarizes everything new in Claude Opus 5, including thinking on by default, mid-conversation tool changes, and a breaking change to when thinking can be disabled.
19Claude Opus 5 is a step-change improvement over Claude Opus 4.8, with the largest gains in deep reasoning, agentic and long-horizon tasks, and test-time compute scaling. This page summarizes everything new in Claude Opus 5, including mid-conversation tool changes and two breaking changes for code running on Claude Opus 4.8: thinking is on by default, and thinking can be disabled only at effort `high` or below.
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2121[What's new in Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/whats-new-opus-5)
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