What changed
Anthropic shipped Claude Code 2.1.277 on September 18, 2026, and in a project with no CLAUDE.md it now reads AGENTS.md instead 1. The npm tarball went up at 2026-09-18T16:22:26.548Z 5. The reader is a built-in plugin called agents-md, driven by a Project instructions setting whose default is claude-md-or-agents-md 2.
What the default resolves
That default picks one file and drops the other. A CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md in your working directory or any directory above it makes Claude read those and leave AGENTS.md aside, while your user-level CLAUDE.md, your organization’s managed one and .claude/rules/ keep loading beside it 2. The trap is the local file: the docs state that adding a CLAUDE.local.md for your own uncommitted notes stops Claude reading the team’s AGENTS.md, for you alone 2. The mode that reads both, claude-md-and-agents-md, exists, but Claude Code ignores it in project and local settings files 2. A team cannot commit that fix. Each developer sets it, or an organization pushes it through managed settings 2.
What I would actually commit
I keep the boring path the docs already bless: a CLAUDE.md whose whole body is the import.
@AGENTS.md
It fires InstructionsLoaded hooks and lists the file in /memory and /context, neither of which an AGENTS.md read through the setting does 2, and it works in the sessions above. Keeping the import never makes Claude read AGENTS.md twice, whichever value you choose 2.
Impact on your team
Check your install channel first. Reading the npm registry on September 19, I saw the stable dist-tag pointing at 2.1.267 5, below the v2.1.277 floor the docs set 2, while latest was already 2.1.278 5. If you install from stable, you do not have this yet. The decision sits elsewhere: your AGENTS.md is now read by Claude Code too, so anything written in it for a different agent is now Claude’s instruction set. Reread it once with that in mind. The project site claims over 60k open-source projects carry the format 3, and WindowsForum makes the reading I would hand a platform team: a fallback does not give you the shared policy file you think you are adopting 4.