One read of Claude Developer Platformapi-20260828T173708Z
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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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2323## Compare models
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25If you're unsure which model to use, start with [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview) for complex agentic coding and enterprise work; for the highest available capability, use [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/overview). All current models support text and image input, text output, multilingual capabilities, vision, and tool use; each model’s page lists the platforms it is available on.
25If you're unsure which model to use, start with [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview) for complex agentic coding and enterprise work; for the highest available capability, use [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/overview). All current models support text and image input, text output, multilingual capabilities, vision, and tool use; each model's page lists the platforms it is available on.
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2727| Feature | Claude Fable 5 | Claude Opus 5 | Claude Sonnet 5 | Claude Haiku 4.5 |
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7676* **Performance:** Top-tier results in reasoning, coding, multilingual tasks, long-context handling, honesty, and image processing. See [Prompting best practices](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/claude-prompting-best-practices) for general and model-specific prompting guidance.
7777* **Engaging responses:** Claude models are ideal for applications that require rich, human-like interactions. If you prefer more concise responses, adjust your prompts to guide the model toward the desired output length. Refer to the [prompt engineering guides](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering) for details.
78* **Output quality:** When migrating from a previous model generation, you may notice larger improvements in overall performance. If you're on Claude Opus 4.8 or earlier, see [Migrating to Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/migration-guide#migrating-from-claude-opus-4-8-to-claude-opus-5).
78* **Output quality:** When migrating from a previous model generation, you may notice larger improvements in overall performance. If you're on Claude Opus 4.8 or earlier, see [Migrating to Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/migration-guide).
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8080## Get started with Claude
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