Anthropic updates Claude Code to support AGENTS.md file, joining cross-tool AI coding standard

Anthropic shipped Claude Code version 2.1.277 on September 18, introducing native support for AGENTS.md project instruction files. The update means Claude Code will now automatically read an AGENTS.md file whenever a project lacks the tool’s proprietary CLAUDE.md format, eliminating a friction point that had quietly annoyed developers juggling multiple AI coding agents. Before this release, Claude Code only understood its own CLAUDE.md files for project-level instructions. Developers who also used OpenAI Codex, GitHub Copilot, Gemini CLI, or other AI coding agents had to maintain separate instruction files or resort to workarounds like symlinks and one-line imports that pointed Claude Code toward an AGENTS.md file. The new fallback system is straightforward: if Claude Code doesn’t find a CLAUDE.md file (or any of its variants) in the project hierarchy, it reads AGENTS.md instead. Users can also configure their setups to prioritize one format over the other, or use both simultaneously. One caveat worth noting: the AGENTS.md fallback is not currently available on Bedrock, Vertex, or Foundry. Developers using those platforms will need to stick with the CLAUDE.md format for now. AGENTS...