Beating the Style Detector: Three Hours of Agentic Research on the AI-Text Arms Race

TL;DR

This study reproduces and extends an NLP experiment on style transfer, demonstrating that modern LLMs can significantly reduce detectable AI-generated text and highlighting an ongoing AI-text detection arms race.

Contribution

It provides a reproducible framework for evaluating style transfer and detection, showing LLMs' ability to evade detection with moderate effort and releasing all related code and data.

Findings

GPT-5.5 and Claude Opus 4.7 close 71-75% of the style gap to same-author ceiling.

Detection models achieve high AUC scores, but are confounded by length and style.

Adversarial feedback reduces detection margins and enables evasion.

Abstract

Reproducing an empirical NLP study used to take weeks. Given the released data and a modern agentic-research harness, we redo every experiment of a recent ACL\,2026 study on personal-style post-editing of LLM drafts -- and add three new ones -- with the human investigator acting only as a reviewer-in-the-loop. We reproduce all seven preregistered hypotheses and recover the paper's headline correlation between perceived self-similarity and embedding-measured self-similarity to three decimal places ($r{=}{+}0.244$, $p{<}10^{-8}$, $n{=}648$). Under a leakage-free held-out protocol, GPT-5.5 and Claude\,Opus\,4.7 close $71$--$75\,\%$ of the style gap to the same-author ceiling on $324$ paired tasks, against $24\,\%$ for the human post-edit, and beat the human post-edit on $\sim$$80\,\%$ of tasks. We then frame the same data as an AI-text detection arms race. A leave-authors-out linear SVM on LUAR-MUD embeddings reaches AUC $0.93$--$1.00$ across approaches; six diagnostics show that GPT-5.5 detection is mostly a length confound while Opus detection is a genuine stylistic signature. Given $T{=}20$ feedback iterations against the frozen detector, an Opus agent flips two of five held-out test mimics to the human half-space and shrinks every margin by an order of magnitude. With moderate effort against a known detector, a frontier LLM can already efficiently lower its own AI-detection probability. All code, $648$ mimic drafts, trained detectors, diagnostics, and adversarial trajectories are released.