September 17, 2026
Nearly half of the sources AI models cited in September were new since August
The month-over-month citation churn promised in the August citation study is now published. Across the 193 categories the Index collected in both editions, a median 48 percent of the source domains cited in September had not been cited in August. The steadiest category changed 17 percent of its sources, the most volatile 68 percent. Pooled across all 8,458 category and domain pairs the figure is 49 percent. Sources are counted as distinct domains per category across every AI model the Index asks, from each edition’s own citation record; a category cited by fewer than 20 domains is not published.