Claude Code falls back to AGENTS.md when a folder has no CLAUDE.md

single source· 1 articles · confidence: medium · first seen 2026-09-18 19:09 UTC

What this means for you

If your repository already carries an AGENTS.md, you can drop the parallel CLAUDE.md on 2.1.277 and later — Claude Code falls back to AGENTS.md only when CLAUDE.md is missing. Everything else waits: mods, the mechanism this is built on, have no date, so there is nothing to migrate to yet.

Anthropic's Claude Code will read AGENTS.md in a folder that has no CLAUDE.md, starting with version 2.1.277, according to a statement from Thariq Shihipar quoted by Simon Willison. The fallback is built on Claude Code mods, described as an upcoming way to customise the harness — the scaffolding around the model that supplies files, runs commands and manages context. Projects that keep an AGENTS.md no longer need a parallel CLAUDE.md for Claude Code to pick the instructions up. No date has been given for mods.

Key facts

  • ·Claude Code version 2.1.277 adds support for AGENTS.md. source
  • ·Claude checks for AGENTS.md only when no CLAUDE.md exists in the folder. source
  • ·AGENTS.md support is built on Claude Code mods, described as an upcoming way to customise the Claude Code harness. source
  • ·The change was stated by Thariq Shihipar and quoted by Simon Willison on 18 September 2026. source

What the sources say

  • Simon Willison (press) — Reproduces a short statement from an Anthropic engineer announcing the fallback and the mods it depends on.

Sources

The original reporting. Follow these — they did the work.

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