Do Context Files Help Coding Agents? A Two-Agent Ablation Study on Real Repositories

Prakhar Khatri


Abstract
Persistent context files (AGENTS.md, CLAUDE.md) are standard practice for guiding AI coding agents, yet evidence for their effectiveness is contradictory. We present a controlled ablation of context-injection strategy across two frontier agents (Claude Code and Codex), 17 real tasks from 3 repositories, and 288 evaluated runs with gold-test evaluation. Context strategy does not measurably move correctness on either agent (bounded to ≤10–15pp via equivalence testing). A failure-mode triage reveals why: agents fail on implementation skill—feature design, pattern selection, exact wiring—not missing repository knowledge that a context file could supply; a manipulation probe confirms the real AGENTS.md never converts a near-miss to a pass on either agent. We further show that borderline task difficulty is agent-specific (Spearman 𝜌=0.75), offering a candidate explanation for prior contradictions: single-agent studies draw tasks from different agents’ informative bands. We release all code, data, and analysis.
Anthology ID:
2026.realm-1.5
Volume:
Proceedings of the Second Workshop for REsearch on Agent Language Models (REALM 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Ehsan Kamalloo, Nicolas Gontier, Nikolai Rozanov, Maryam Hashemzadeh, Akhil Arora
Venues:
REALM | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
57–67
Language:
URL:
https://aclanthology.org/2026.realm-1.5/
DOI:
Bibkey:
Cite (ACL):
Prakhar Khatri. 2026. Do Context Files Help Coding Agents? A Two-Agent Ablation Study on Real Repositories. In Proceedings of the Second Workshop for REsearch on Agent Language Models (REALM 2026), pages 57–67, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Do Context Files Help Coding Agents? A Two-Agent Ablation Study on Real Repositories (Khatri, REALM 2026)
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PDF:
https://aclanthology.org/2026.realm-1.5.pdf