​01 Advisors (01A) is a venture capital firm founded in 2018 by former Twitter executives Dick Costolo and Adam Bain, with David Fischer joining as a partner in 2023. Based in San Francisco and New York City, 01A focuses on investing in technology companies that have achieved product-market fit, typically at Series A and B stages. The firm's partners leverage their extensive experience in scaling companies to assist founders in transitioning from building a product to building a company.