The breaking changes vs. Opus 4.8 are interesting [1] 1. Thinking on by default: On Claude Opus 4.8, requests without a thinking field run without thinking; on

The breaking changes vs. Opus 4.8 are interesting [1] 1. Thinking on by default: On Claude Opus 4.8, requests without a thinking field run without thinking; on Claude Opus 5, the same requests run with adaptive thinking. 2. Disabling thinking is capped at high effort: You can still turn thinking off with thinking: {type: "disabled"}, but only at an effort level of high or below. [1] https://platform.claude.com/docs/en/about-claude/models/migration-guide#migrating-from-claude-opus-4-8-to-claude-opus-5 https://platform.claude.com/docs/en/about-claude/models/migr...