Claude Code now reads AGENTS.md when CLAUDE.md is absent

Anthropic shipped AGENTS.md support in Claude Code on 18 September 2026. When a project has no CLAUDE.md file, Claude Code now reads AGENTS.md instead, the shared instructions file that OpenAI's Codex, Cursor, Devin and more than a dozen other coding agents already read. The change appeared in the Claude Code changelog the same day, among a long list of stability and gateway fixes.

AGENTS.md is a plain Markdown file that sits next to a project's README and holds the setup commands, code style rules and testing instructions a coding agent needs to work in that repository. Claude Code previously read only its own CLAUDE.md; as of 18 September 2026 it falls back to AGENTS.md when CLAUDE.md is missing, so one instructions file now works across Claude Code, Codex, Cursor and the rest.

What changed

• Claude Code's 18 September 2026 changelog entry reads: "Added AGENTS.md support: in a project with no CLAUDE.md, Claude Code reads AGENTS.md instead; change it under 'Project instructions' in /config", and notes the fallback is not yet available on Bedrock, Vertex or Foundry.
• AGENTS.md itself was released in August 2025 by OpenAI's Codex team working with Amp, Google's Jules, Cursor and Factory. According to agents.md, it is now used in more than 60,000 open source repositories, and agents from Windsurf, Devin, Augment Code, JetBrains' Junie, Gemini CLI, GitHub Copilot's coding agent, goose, Aider, Warp, Zed, Kilo Code, Amp, VS Code and opencode all read it.
• Since December 2025, AGENTS.md has been stewarded by the Agentic AI Foundation, a directed fund under the Linux Foundation that OpenAI, Anthropic and Block founded, with Google, Microsoft, AWS, Bloomberg and Cloudflare as supporters. Anthropic's own Model Context Protocol and Block's goose are the foundation's other two founding projects.
• A GitHub feature request asking Claude Code to support AGENTS.md had been open since 21 August 2025 before this release closed it.

Why it matters for agent builders

Teams that maintained both a CLAUDE.md and an AGENTS.md in the same repository, one for Claude Code and one for every other agent, can now drop the duplicate: Claude Code reads AGENTS.md itself once CLAUDE.md is gone. The fallback only fires when CLAUDE.md is absent, so a repository that still keeps both files keeps sending Claude Code to CLAUDE.md; consolidating means removing or merging the old file, not just adding the new one. For anyone running Claude Code through Bedrock, Vertex or Foundry, the changelog says the fallback is not yet available on those platforms, so the split setup stays for now on those deployments.

What to watch

The changelog leaves open when Bedrock, Vertex and Foundry deployments get the same fallback, and whether Anthropic pushes teams to retire CLAUDE.md entirely now that AGENTS.md support exists and the file to load can already be changed under "Project instructions" in /config.

Key takeaways

• Claude Code reads AGENTS.md instead of CLAUDE.md when a project has no CLAUDE.md file, a change shipped 18 September 2026.
• AGENTS.md was released by OpenAI in August 2025 with Amp, Google's Jules, Cursor and Factory, and is now used in more than 60,000 open source repositories.
• The Agentic AI Foundation, a Linux Foundation project OpenAI, Anthropic and Block founded in December 2025, stewards AGENTS.md alongside Anthropic's Model Context Protocol and Block's goose.
• The AGENTS.md fallback is not yet available on Claude Code deployments through Bedrock, Vertex or Foundry.
• A GitHub feature request for this exact change had been open since 21 August 2025.

FAQ

What is AGENTS.md?

AGENTS.md is a plain Markdown file that sits next to a project's README and gives a coding agent the build steps, code style rules and testing instructions it needs to work in that repository, without cluttering the README that human contributors read.

Does Claude Code still support CLAUDE.md?

Yes. Claude Code reads CLAUDE.md first and only falls back to AGENTS.md when a project has no CLAUDE.md file. A project that keeps both files still sends Claude Code to CLAUDE.md.

Which other coding agents read AGENTS.md?

According to agents.md, supported tools include OpenAI's Codex, Google's Jules and Gemini CLI, Cursor, Devin, Factory, Amp, Aider, Zed, Kilo Code, opencode, goose and GitHub Copilot's coding agent, among others.

Source: Claude Code changelog Discussion: Hacker News

Developers weighing Claude Code against other coding agents can check its listing on Claude Code at aiagentslisting.com.