Act on this, mostly signal

Codex reads AGENTS.md once at startup, so check these five things

What to do

Check for an AGENTS.override.md in the same directory, since it makes Codex ignore AGENTS.md.

Why

Codex assembles AGENTS.md once at startup, and the official OpenAI doc was checked October 20.

What the research found

Note.com guide, citing the official OpenAI AGENTS.md doc (checked Oct 20, 2026), says Codex assembles AGENTS.md once at startup, reads a home override file first, and ignores AGENTS.md when AGENTS.override.md sits in the same directory.

Claims and how well the evidence supports them

Codex assembles AGENTS.md instructions only once at startup, per execution or per session 98%
AGENTS.override.md in the same directory causes AGENTS.md to be ignored 98%
When no project root (Git root) is found, Codex only reads the current directory AGENTS.md 96%

Evidence

note.com https://note.com/codex_studio/n/nad48d2cf8706?hl=en
learn.chatgpt.com https://learn.chatgpt.com/docs/agent-configuration/agents-mdIn

Actionability rated high.