Quoting Thariq Shihipar

We're adding support for AGENTS.md to Claude Code.

Starting today in version 2.1.277, if there is no CLAUDE.md in a folder, Claude will check for and use AGENTS.md.

AGENTS.md support is built off of Claude Code mods, our upcoming way to customize the Claude Code harness.

This is a built-in mod, but you’ll be able to build custom versions of project instructions yourself as you’d like too.

You can see the source for the mod here!

— Thariq Shihipar, there are more mods here