We scored the full text of 12,750 arXiv papers and found that about a third of new ones read as machine-written. Here is the method, the results, and an honest account of the limitations.Share of new arXiv papers flagged as machine-written, 2021 to 2026, at a threshold calibrated so pre-ChatGPT papers flag at 0.4%. The eight slate points are the pre-LLM control months; the band is a bootstrap 95% interval. Share of papers flagged as machine-written by field, over the 12 months to July 2026 (abou...