Stale Instruction Files Override the Code in Coding Agents: A One-Sentence Fix

Xiaonan Xu, Wenjing Wu · 2026 · arXiv

DOI: 10.48550/arXiv.2610.30571 · open-access PDF

Abstract

Purpose: Coding agents follow a project's instruction file, such as CLAUDE.md or AGENTS.md, even when it disagrees with the existing code and even when they notice the disagreement. We measure this behaviour and test whether one sentence in the user's own instruction file makes agents follow the code instead. Methods: We built 40 Python projects in which the instruction file asks for one convention while the existing code uses another, for example print instead of logging. Claude Code and Codex CLI added a feature to each project, with and without a sentence in the user-level instruction file

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