CL-SN55 941 —
GPT-61S 890 —
GPT-56T 861 —
GPT-6S 837 -1.2%
CL-OP55X 831 -1.4%
MUSE-SPK 804 —
QWEN-38X 795 —
GPT-6A 782 —
CL-OP5H 724 -1.6%
CL-OP5X 722 -1.6%
KIMI-K3X 718 -0.1%
CL-OP46H 707 -1.7%
CL-FAB5H 705 -7.4%
CL-OP55H 705 -1.7%
CL-OP47H 696 -1.7%
GEM-37FH 661 -9.7%
GEM-38FH 656 -4.8%
GPT-56S 578 -0.5%
CL-OP47 543 -0.5%
INKL 531 —
GEM-3P 494 -0.2%
CL-OP46 490 -0.2%
GEM-31P 485 -0.4%
CL-OP48 483 -0.2%
GPT-6L 436 —
CL-SN55 941 —
GPT-61S 890 —
GPT-56T 861 —
GPT-6S 837 -1.2%
CL-OP55X 831 -1.4%
MUSE-SPK 804 —
QWEN-38X 795 —
GPT-6A 782 —
CL-OP5H 724 -1.6%
CL-OP5X 722 -1.6%
KIMI-K3X 718 -0.1%
CL-OP46H 707 -1.7%
CL-FAB5H 705 -7.4%
CL-OP55H 705 -1.7%
CL-OP47H 696 -1.7%
GEM-37FH 661 -9.7%
GEM-38FH 656 -4.8%
GPT-56S 578 -0.5%
CL-OP47 543 -0.5%
INKL 531 —
GEM-3P 494 -0.2%
CL-OP46 490 -0.2%
GEM-31P 485 -0.4%
CL-OP48 483 -0.2%
GPT-6L 436 —
← Back to feed

Anthropic Adds AGENTS.md Fallback to Claude Code, Aligning with OpenAI's Agent Instruction Spec

Anthropic shipped Claude Code version 2.1.277 on September 18 with one ecosystem-significant addition: in any project that has no CLAUDE.md, Claude Code now reads AGENTS.md instead.

The behavior is configurable. Developers can review or change the active instruction file under “Project instructions” in /config. Pinning a specific file takes precedence over the automatic fallback.

One caveat: the feature is not yet available on Bedrock, Vertex, or Foundry. Managed API deployments will follow separately.

Why it matters

AGENTS.md is the instruction file format OpenAI’s Codex and other tools in that ecosystem use to pass project-level configuration to agents. Until now, teams running both Claude Code and OpenAI-adjacent tooling on the same codebase had to maintain two separate instruction files — CLAUDE.md for Anthropic, AGENTS.md for OpenAI.

With this change, a single AGENTS.md works for both. Teams that have already standardized on AGENTS.md can add Claude Code to their stack without touching their existing configuration. Claude Code falls back gracefully: CLAUDE.md takes priority if it exists; AGENTS.md is the next read.

The broader signal

Anthropic adopting a spec originated at OpenAI is unusual. The company has historically maintained its own instruction format and its own tooling conventions. Accepting AGENTS.md as a valid project instruction source signals that the two ecosystems are converging around shared conventions, at least at the developer tooling layer.

For enterprises managing agent fleets across multiple providers, reducing the instruction-file surface area from N formats to one is a concrete operational improvement — fewer files to audit, fewer drift vectors.

The feature ships immediately in Claude Code 2.1.277. Developers on Bedrock, Vertex, or Foundry will need to wait for a separate rollout.