Opus 4.7 does not support disabling adaptive thinking (web, Claude Code). [1] Like the OP, I experienced similar issues and I'm glad that they brought back the ability to disable adaptive thinking in Opus 4.8.
[1] https://code.claude.com/docs/en/model-config#adaptive-reason...
> Opus 4.7 and later always use adaptive reasoning. The fixed thinking budget mode and `CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING` do not apply to them.
> Opus 4.7 and later
The source of truth should be the API docs which make it clear 4.8 didn't bring back extended thinking: https://platform.claude.com/docs/en/about-claude/models/over...
Any UI settings probably just map to changing the effort nudge on adaptive thinking
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Thank you for pointing this out.