Anthropic released Claude Code version 2.1.277 on September 18, 2026. The update introduces native support for the AGENTS.md instruction format, which is currently used in over 60,000 repositories.
Previously, Claude Code relied exclusively on its proprietary CLAUDE.md files. The new system allows the tool to automatically read AGENTS.md as a fallback if no CLAUDE.md file is detected in the project hierarchy.
This update aligns Claude Code with other AI coding tools like GitHub Copilot, OpenAI Codex, and Gemini CLI, which already support the AGENTS.md standard. Users can configure their preferences to prioritize either format or use both.
The AGENTS.md fallback is currently unavailable for developers using Bedrock, Vertex, or Foundry platforms. These users must continue to use the CLAUDE.md format.
On September 17, 2026, one day prior to this release, Anthropic announced a redesign of Claude Code Projects aimed at improving the coordination of multi-agent threads.
