The median open-source repo pays no "AI review tax" (data from 5,388 repos)

The Index The Review Tax Index The claim you will hear is that AI-written code costs more review everywhere. The data says something more useful: the cost is a split — it lands hard on some repositories and not at all on others. This page measures where. Repositories read 5,388 Merged PRs analyzed 444,225 Zero attribution 56% no detectable agent authorship at all Agent-native repos 15% of attributed repos, 20%+ of merged work carries attribution The split The measures run over the 2,353 repositories with detectable attribution and at least 10 analyzed PRs — a review-cost ratio needs an attributed side to exist. Within each, attributed work is measured against the rest of the same repository — same reviewers, same conventions, same era. A multiple above 1x means the attributed side took more; below means it took less. Time to merge, attributed / rest 354 repos above 1x 874 at or below 1x 0.5x median 29% of comparable repos pay more review on attributed work; 71% pay the same or less. Middle half of the population: 0.2x to 1.2x. Review rounds, attributed / rest 6 repos above 1x 13 at or below 1x 0.6x median 32% of comparable repos pay more review on attributed work; 68% pay the same or less. Middle half of the population: 0.2x to 1.2x. Where the tax lands Median detected share across the attributed repositories is 3% — and that is a floor, not a share: attribution comes only from marks a tool leaves on a commit, so inline-completion work is invisible by construction. Across the full population the median is zero — most repositories read carry no attribution at all. By primary language SegmentReposMedian detected shareTime to mergeReview rounds TypeScript4423%0.4x— Python3614%0.5x— Go3023%0.5x— Rust2372%0.7x— JavaScript2172%0.4x— C++1703%0.4x— Java1312%0.3x— C#1296%0.3x— C982%0.4x— PHP872%0.3x— Swift683%0.5x— Kotlin532%0.4x— Ruby493%0.5x— A dash means the segment has too few comparable repos for that measure to publish — a median over a handful of ratios is noise wearing a number. By project size SegmentReposMedian detected shareTime to mergeReview rounds 50k+ stars2384%0.4x— 20k-50k stars6243%0.5x— 10k-20k stars6883%0.4x— 5k-10k stars7753%0.5x— 2k-5k stars261%—— A dash means the segment has too few comparable repos for that measure to publish — a median over a handful of ratios is noise wearing a number. How to read this Attributed vs rest, never AI vs human. The comparison group contains AI-assisted work that leaves no trace, which narrows every gap shown here rather than widening it. The sample self-selects twice. These are repositories someone chose to scan plus a curated backfill of well-known projects — a population of repos people care about, not a random sample of software. Withheld beats invented. Repos below 10 analyzed PRs do not count; segments below 12 comparable repos publish no median. The Index republishes quarterly. Repos already read keep their history, so future editions carry trend lines — not just where the tax lands, but where it is moving. Full method and every limitation: /methodology. Place your own repo against this population: /scan.