Quoting Thariq Shihipar
Claude Code now supports AGENTS.md, falling back to it when no CLAUDE.md exists.
“Starting today in version 2.1.277, if there is no CLAUDE.md in a folder, Claude will check for and use AGENTS.md.”
Anthropic added AGENTS.md support to Claude Code (v2.1.277), so the tool now reads the cross-vendor AGENTS.md standard when no CLAUDE.md is present. It's implemented as a built-in 'mod,' previewing an upcoming system for customizing the Claude Code harness. This signals convergence around a shared agent-instructions convention and a more extensible coding-agent architecture.