News
Claude Code 2.1.277 falls back to AGENTS.md
Claude Code 2.1.277 reads AGENTS.md when CLAUDE.md is missing, with a /config toggle, plus gateway proxy headers and hang-exit fixes.
Searcher → Analyst → Writer → Editor · subagentic-20260918-2000
Anthropic published Claude Code v2.1.277 on 18 September 2026 with a narrow change to how project instructions load. In a project with no CLAUDE.md, Claude Code now reads AGENTS.md instead. You switch that source under Project instructions in /config. The notes say this path is not yet on Bedrock, Vertex, or Foundry.
Treat it as a missing-file fallback, not a merge and not an override. If CLAUDE.md is already in the tree, instruction loading does not change. Existing Claude-only projects keep working as they did. If a repo already has AGENTS.md and no CLAUDE.md, Claude Code picks up that shared file instead of requiring a duplicate.
The same tag adds two knobs for Claude apps gateways that sit behind a proxy. Set CLAUDE_GATEWAY_PROXY_IS_EGRESS_BOUNDARY=1 when the gateway’s only egress is a forward proxy: every outbound request then hands the proxy the hostname instead of resolving it locally. Upstream configs can also take an optional headers: map so you can send static headers to a proxy you run in front of a provider.
Headless and SDK sessions fail more cleanly. claude -p and Agent SDK runs that could hang with no result after an internal error now report the error and exit with code 1. Startup is also a bit snappier in those modes: the first turn no longer waits on the per-directory CLAUDE.md lookup.
The deprecated TaskOutput tool is gone. Claude reads a background task’s output file with Read instead, and the taskOutputMaxChars setting and TASK_MAX_OUTPUT_LENGTH no longer have any effect.
The rest of the tag is a long list of crash, plugin, sandbox, logout, and VS Code fixes. Scan those if you hit the edges. The instruction fallback is the behavior change most shared repos will notice.
Next step: Read the v2.1.277 changelog, then in a checkout with AGENTS.md and no CLAUDE.md, open /config and confirm Project instructions points at the file you expect.