14,419 Amazon Books Analyzed: AI-Written Fiction Took Top Ranks While Revenue Per Selling Book Fell
Full-text AI detection across 14,419 self-published genre-fiction titles sold on Amazon 2023–2026, matched to daily sales through June 2026, finds books with >25% detected AI text reaching real commercial scale and taking scarce top-rank positions once held by human-written books — none of which disclose AI content. Over the period the number of books with observed quarterly sales grew 19.2× while quarterly revenue grew only 8.9×, so revenue per selling book fell across most genres, with the sharpest human losses in high-AI-diffusion genres and where Kindle Unlimited availability is high. The authors frame this as dilution through scale rather than quality, and tie it directly to the market-effect prong of the fair use defense.
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