Anthropic tells Opus 5.5 users to delete “think hard” lines

In Anthropic’s chat testing, cutting a “think carefully” line made replies start sooner, with no clear drop in quality. The new guide for Claude and Claude Code explains why. Opus 5.5 always thinks before it replies and decides how much.

Most of the tips are about long runs. Put the whole task in one message with a finish line like “the tests pass.” Add a CLAUDE.md rule on when to stop and ask. Keep the task list in a file, because a file survives when Claude Code summarizes older turns.

Opus 5.5 ships with new bio and cyber safeguards, and most flagged messages move to an older model. You can switch back with /model. Anthropic admits the safeguards sometimes flag legitimate work.

For code review, one early tester said Opus 5.5 at its lowest effort caught more bugs than Opus 5 at high effort, with fewer false alarms.