AGENTS.md Becomes a Fallback for Claude Code Project Instructions
AGENTS.md is now supported by Claude Code: when a project has no CLAUDE.md, Claude Code reads AGENTS.md instead. The change appears in the 2.1.277 release and reduces extra configuration for repositories that already use the broader agent-instructions convention.
What the Compatibility Update Means
Maintainers can keep project-level coding conventions, workflows, and other agent guidance in AGENTS.md without creating a duplicate CLAUDE.md solely for Claude Code. The relationship is explicitly a fallback: the release note says AGENTS.md is read when CLAUDE.md is missing, but does not say that the two files are merged or applied together.
Platform Availability Remains the Key Limitation
The feature is not yet available on Bedrock, Vertex, or Foundry. The changelog also does not specify the full file-discovery hierarchy, conflict behavior, or priority rules across environments. Teams should therefore verify the behavior against their installed version and deployment target before changing established project instructions. The release includes many stability and error-handling fixes, but those fixes should not be read as expanding AGENTS.md availability.