GoKawiilWe 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 (about 300 papers per field).
A false-positive floor
There is a genre of headline that says "N% of X is now AI," and most are not worth reading, because the detector behind the number also flags some share of genuine human writing. If a tool marks 40% of new papers as machine-written but also marks 20% of papers written before ChatGPT existed, the real story is the 20% nobody mentioned.
So we built the study around that objection. Our detector, described here, is calibrated for academic writing; at a 0.4% false-positive rate it clears 99.6% of genuine pre-LLM scientific text and recovers 85% of AI academic text. We made that false-positive rate the anchor. We took papers submitted in 2021 and 2022, before ChatGPT, treated them as ground-truth human, and set the flag threshold so that exactly 0.4% of them trip it. That line is the floor. Every number we report is a share of papers above a threshold where genuine pre-LLM writing sits, by construction, at 0.4%. The pre-ChatGPT years then act as a built-in control: if the rise were an artifact of the detector, 2021 and 2022 would flag as high as 2026. The first figure shows they do not.
What we measured
We sampled ten field groups, roughly 25 papers per field per month, from January 2023 to July 2026, plus eight control months across 2021 and 2022, for 12,750 papers in total. For each one we pulled the version-1 PDF, so a paper revised in 2026 cannot leak modern text back into its 2023 slot. We scored the full body text instead of the abstract, because abstracts understate the signal: we have seen the same paper score under 20% on its abstract and over 70% on its body. Every reported figure carries a bootstrap 95% confidence interval.
Results
The flagged share is flat at 0.4% through 2021 and 2022, lifts off within months of ChatGPT, and climbs in two waves to about 32% over the most recent complete quarter, peaking near 39% in early 2026. The spread across fields is large, and it is the table and the second figure that carry it. The values below are each field's flagged share over the 12 months to July 2026, alongside its pre-LLM control level.
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