Claude Code reads AGENTS.md now, but one personal file you might add for yourself quietly switches that off

Since version v2.1.277 (September 18), Claude Code now supports AGENTS.md for project instructions, allowing repositories configured for Codex or Cursor to function without needing a CLAUDE.md file. This update is a positive change, though understanding the default file reading rules is important as some can fail silently. The chat interface presents a similar issue where instructions saved in one assistant do not transfer to another, highlighting the utility of external tools like AI Toolbox for consistent prompt management across various AI platforms such as ChatGPT, Claude, Gemini, and Grok.

This report highlights Claude Code's new support for AGENTS.md since v2.1.277, unlike previous versions that required CLAUDE.md, and details how to manage this change.