These models don't take claude.md, Claude Code does, and claude.md still get fed to these models if you're using Claude Code.

That said, prompting on opus 5 needs new technique: https://platform.claude.com/docs/en/build-with-claude/prompt...

Thanks; the issue likely stemmed from the translation software used previously. I’ve seen many people online mention that removing skills like "superpowers" reduces token consumption and shortens completion times. I also read that Anthropic removed over 80% of the system prompts for Claude Code. I’m interested in finding out how to adjust `claude.md` and the installed skills to better optimize performance for the Opus 5 and Fable 5 models.