Anthropic updates Claude Code to support AGENTS.md file, joining cross-tool AI coding standard

Anthropic shipped Claude Code version 2.1.277 on September 18, adding native fallback support for AGENTS.md project instruction files so the tool reads the community format whenever a project lacks its proprietary CLAUDE.md file. AGENTS.md is now used in over 60,000 repositories and is already read by OpenAI Codex, GitHub Copilot, and Gemini CLI, making Claude Code the last major AI coding agent to adopt it. The fallback is not available on Bedrock, Vertex, or Foundry, and the release followed Anthropic's September 17 redesign of Claude Code Projects for coordinating multi-agent threads.

Anthropic updates Claude Code to support AGENTS.md file, joining cross-tool AI coding standard Claude Code version 2.1.277 adds native fallback support for the community-driven instruction format already used in over 60,000 repositories. Anthropic shipped Claude Code version 2.1.277 on September 18, introducing native support for AGENTS.md project instruction files. The update means Claude Code will now automatically read an AGENTS.md file whenever a project lacks the tool’s proprietary CLAUDE.md format, eliminating a friction point that had quietly annoyed developers juggling multiple AI coding agents. Before this release, Claude Code only understood its own CLAUDE.md files for project-level instructions. Developers who also used OpenAI Codex, GitHub Copilot, Gemini CLI, or other AI coding agents had to maintain separate instruction files or resort to workarounds like symlinks and one-line imports that pointed Claude Code toward an AGENTS.md file. The new fallback system is straightforward: if Claude Code doesn’t find a CLAUDE.md file or any of its variants in the project hierarchy, it reads AGENTS.md instead. Users can also configure their setups to prioritize one format over the other, or use both simultaneously. One caveat worth noting: the AGENTS.md fallback is not currently available on Bedrock, Vertex, or Foundry. Developers using those platforms will need to stick with the CLAUDE.md format for now. AGENTS.md is a tool-agnostic Markdown file that tells AI coding agents how to behave within a given project. The format has spread rapidly. Over 60,000 repositories now include an AGENTS.md file, and major AI coding tools have adopted it as a recognized standard. OpenAI Codex reads it. GitHub Copilot reads it. Gemini CLI reads it. Claude Code was the notable holdout, preferring its own proprietary format. AI, tech, and the markets they move—in one daily briefing. Daily. Free. Join 34,000+ readers across crypto, finance, and policy. The AGENTS.md fallback doesn’t eliminate CLAUDE.md, which still offers Claude-specific configuration options, but it does mean that a single AGENTS.md file can now serve as the baseline instruction set across every major AI coding agent on the market. The AGENTS.md support didn’t arrive in isolation. One day earlier, on September 17, Anthropic announced a redesign of Claude Code Projects focused on coordinating multi-agent threads. The symlink-and-import workarounds that developers previously relied on were functional but fragile. They required manual setup, broke easily in CI/CD pipelines, and confused new team members who didn’t understand why a one-line file was importing instructions from a differently named Markdown file elsewhere in the repo. Native fallback support eliminates that entire category of setup headaches. For teams evaluating AI coding tools, the practical impact is immediate. A project can now ship a single AGENTS.md file and have it work across Claude Code, Copilot, Codex, and Gemini CLI without any tool-specific configuration. Teams that want to fine-tune Claude Code’s behavior can still layer a CLAUDE.md file on top, but the baseline works out of the box. Disclosure: This article was edited by Editorial Team. For more information on how we create and review content, see our Editorial Policy https://cryptobriefing.com/editorial-policy/ .