Claude Code Starts Reading AGENTS.md, Nine Months Late

Claude Code began reading AGENTS.md files on Friday, shipping the change in version 2.1.277 for any project that has no CLAUDE.md of its own.

The change appears in the command-line tool's public changelog, with no accompanying blog post. The entry reads in full: "Added AGENTS.md support: in a project with no CLAUDE.md, Claude Code reads AGENTS.md instead; change it under 'Project instructions' in /config (not yet on Bedrock, Vertex or Foundry)." Anthropic's own npm registry listing shows 2.1.277 published at 4:22 p.m. Eastern on Friday.

What AGENTS.md is and who built it

AGENTS.md is a plain-text convention: a file named AGENTS.md sits in a repository's root and tells a coding agent how to build it, test it and follow its conventions, in place of a human-facing README. The project's own site says the format "emerged from collaborative efforts across the AI software development ecosystem, including OpenAI Codex, Amp, Jules from Google, Cursor, and Factory." Claude Code is not on that list. OpenAI released the format in August 2025, and the site puts current adoption at more than 60,000 open-source projects and more than 20 coding tools, among them Codex, Cursor, Gemini CLI and GitHub Copilot.

The foundation Anthropic already co-founded

On Dec. 9, 2025, the Linux Foundation announced the formation of the Agentic AI Foundation, a neutral body to govern open agent infrastructure. Its three founding contributions were OpenAI's AGENTS.md, Block's goose and Anthropic's own Model Context Protocol, the standard Claude Code uses to connect to external tools. Nick Cooper, a member of the technical staff at OpenAI, said in the announcement that "for AI agents to reach their full potential, developers and enterprises need trustworthy infrastructure and accessible tools to build on." Anthropic has sat on the foundation's governance alongside OpenAI for more than nine months. Its own command-line tool did not read the foundation's other headline format until Friday.

What still does not get it

The changelog's parenthetical excludes three of Claude Code's enterprise deployment paths. A team running Claude Code through Amazon Bedrock, Google's Vertex AI or Microsoft Foundry gets no AGENTS.md support yet; the feature is live only for the direct API and subscription apps. Anthropic's own npm registry data shows the same split at the release-channel level: the registry's latest and next tags point to 2.1.277, but the stable tag published to package managers still points to 2.1.267, nine builds behind. A team pinned to stable will not get AGENTS.md support with today's install.

Claude Code deployment	AGENTS.md support as of 2.1.277
Direct API / subscription apps	Yes
Amazon Bedrock	Not yet
Google Vertex AI	Not yet
Microsoft Foundry	Not yet

The practical effect for a team that already maintains an AGENTS.md file for Codex or Cursor: Claude Code will now read that same file automatically, without a repository needing a second, Claude-specific instructions file, as long as no CLAUDE.md already exists to take precedence. Anthropic has not said when Bedrock, Vertex or Foundry customers will get the same behavior, or when the stable npm channel will catch up to 2.1.277.

The change lands in a season of fast-moving coding tools: Alibaba shipped IntelliJ support for its own Open Code Review plugin, and a competing tool was separately caught silently uploading users' full Git history to its own servers. A file an agent reads automatically, without a prompt asking permission, is exactly the kind of quiet behavior change that only shows up in a changelog someone has to go looking for.

Anthropic did not publish a separate post explaining the change; the changelog entry is the only public account of it. The next stable release is the milestone to watch for confirmation that the feature has reached every deployment path.