Claude Opus 5.5 official prompting guide

Anthropic has released an official prompting guide for Claude Opus 5.5, a detail that some users may have overlooked. The guide provides important information, such as how changing the top-level effort value between requests invalidates the prompt cache. It suggests using a per-message effort change (beta) to maintain the cache when running individual turns at different effort levels.

This guide is the first official documentation for Claude Opus 5.5, detailing specific technical considerations like prompt cache invalidation that were previously unaddressed.