  Artificial intelligence (AI) assistants such as GitHub Copilot and ChatGPT,
built on large language models like GPT-4, are revolutionizing how programming
tasks are performed, raising questions about whether code is authored by
generative AI models. Such questions are of particular interest to educators,
who worry that these tools enable a new form of academic dishonesty, in which
students submit AI generated code as their own work. Our research explores the
viability of using code stylometry and machine learning to distinguish between
GPT-4 generated and human-authored code. Our dataset comprises human-authored
solutions from CodeChef and AI-authored solutions generated by GPT-4. Our
classifier outperforms baselines, with an F1-score and AUC-ROC score of 0.91. A
variant of our classifier that excludes gameable features (e.g., empty lines,
whitespace) still performs well with an F1-score and AUC-ROC score of 0.89. We
also evaluated our classifier with respect to the difficulty of the programming
problem and found that there was almost no difference between easier and
intermediate problems, and the classifier performed only slightly worse on
harder problems. Our study shows that code stylometry is a promising approach
for distinguishing between GPT-4 generated code and human-authored code.
