Anthropic adds native AGENTS.md support to Claude Code

Anthropic released Claude Code version 2.1.277 on September 18, introducing native support for AGENTS.md. The tool now reads AGENTS.md if CLAUDE.md is absent, and users can configure it to read both files. This update follows pressure from Shopify CEO Tobi Lütke, who criticized the tool's previous limitation to CLAUDE.md. The AGENTS.md format, donated to the Agentic AI Foundation (AAIF) by OpenAI in 2025, is currently used by over 60,000 open-source projects. Anthropic also open-sourced the agents-md mod on GitHub.