Anthropic’s Claude Code now reads the AGENTS.md file format. The change arrived in version 2.1.277, released on September 18. From that point forward, Claude Code looks for an AGENTS.md file in any project directory that does not already contain a CLAUDE.md file.
Before this update, Claude Code recognized only its own CLAUDE.md format. Developers who worked with more than one AI coding assistant had to keep separate instruction files for each tool. The new fallback behavior removes that requirement for many projects. Users can turn the feature on or off under the “Project instructions” setting in the configuration menu. The option is not yet available on Bedrock, Vertex, or Foundry deployments.
AGENTS.md is an open format. The Agentic AI Foundation, under the Linux Foundation, now stewards it. The file gives AI coding agents project-specific guidance—build commands, testing rules, and code style conventions among them. OpenAI first released the format in August 2025 together with its Codex tool. More than 60,000 open-source repositories already use it. Tools that support the format include OpenAI Codex, Google’s Jules, Cursor, and Amp. Claude Code’s adoption places it among the platforms that treat AGENTS.md as a shared standard.
Shared Instructions Across Coding Agents
The update solves a practical problem many teams faced. Anyone who used both Claude Code and another assistant previously had to maintain duplicate instruction files or rely on workarounds such as symbolic links and import directives. With the new fallback, a single AGENTS.md file can serve as the common instruction set for most major coding agents.
The move also fits a larger pattern of convergence among AI tools. Anthropic introduced the SKILL.md agent skills format in late 2025. OpenAI and Microsoft later adopted that format as well. The same push toward shared conventions now appears in the handling of project-level instructions.
Current Limits of the Support
Support for AGENTS.md in Claude Code still has boundaries. The tool does not yet read the .agents/skills directory structure that forms part of the full AGENTS.md specification. The fallback also activates only when no CLAUDE.md file is present. Projects that already rely on Anthropic’s proprietary format continue to use that file exclusively. Developers who need both formats can import AGENTS.md from inside a CLAUDE.md file.