Claude Code now falls back to AGENTS.md, easing multi-agent repos

Claude Code will now read a repository's AGENTS.md file when no Claude-specific instruction file exists, closing a gap for teams that run several AI coding agents against the same codebase. The change shipped in Claude Code 2.1.277, announced 18 September 2026 by the Claude Code team: if a folder has no CLAUDE.md, Claude will check for and use AGENTS.md instead.

A fallback, not a takeover

The behavior only applies when no Claude-specific file is present. If Claude Code finds a CLAUDE.md, a .claude/CLAUDE.md, or a CLAUDE.local.md anywhere along the path to the working directory, that file wins and AGENTS.md is ignored. Where none of those exist, AGENTS.md can supply the project's coding rules, build steps and test requirements instead. The feature ships as a built-in plugin, and teams can adjust the behavior — CLAUDE.md only, AGENTS.md as fallback, both loaded together, or a restricted source list — through /config, user settings or managed settings.

Why repositories accumulate duplicate files

Multi-tool teams often end up with more than one instruction file in the same repo: CLAUDE.md for Claude Code, AGENTS.md for Codex, Cursor and others. They start as copies of each other and drift apart until one of them points an agent at a build command that no longer works. A shared AGENTS.md removes that duplication for repos that don't need Claude-specific instructions.

What to watch before relying on it

• CLAUDE.md still wins by default — teams that want both files honored need to change the instruction-source setting explicitly.
• Support currently has gaps on Bedrock, Vertex and Foundry deployments, so the same repo can resolve instructions differently depending on which provider a teammate runs against.
• A tracked GitHub issue (#96005) flags duplicate instructions when the same guidance also arrives through a second channel, such as an agent harness — worth checking before assuming AGENTS.md alone is authoritative.

For MSPs standardizing on one instruction file across client repos that use mixed agent tooling, this removes a real source of drift — but it's worth confirming which Claude Code provider and version each team runs before treating AGENTS.md as the single source of truth.

Sources: DevOps.com, dev.to.