Y Combinator, known for finding first-time founders, is increasingly shaped by repeat founders, according to new data published today. A Crunchbase News analysis of a Y Combinator dataset covers 454 repeat founders who participated at least twice, encompassing 935 founder-company records from 2005 through 2026. Of these, 94%—or 428 people—went through YC exactly twice, 25 appeared three times, and one person, Justin Kan, went through four times. Founders typically returned after an average gap of 5.1 years, with nearly 30% of return participations within two years, including 38 who returned within the same calendar year, and 61 returns after a decade or more. The raw count of repeat founders peaked in 2025 at 65. Academic research provides context: a 2019 Stanford study found serial entrepreneurs' second firms achieve approximately 55% higher sales than their first, and serial entrepreneur firms generate about 98% greater sales and are around 49% more productive than first-timer firms. A CEPR working paper found serial entrepreneur firms are roughly 50% larger, grow about 20% faster, and are approximately 23% more productive. The YC dataset is not a performance study, but it documents a population investors are now paying attention to.