Sam O'Keefe

Sam O'Keefe is the co-founder and CEO of Flex, the San Francisco fintech often called 'Stripe for HSA/FSA payments.' Flex lets health and wellness brands accept the roughly $150 billion of tax-advantaged health-account money that Americans leave sitting unused every year, turning a confusing benefits process into a one-tap checkout. A two-time Y Combinator founder who previously built fraud and risk software at Unit21 and led startup programs at Google, O'Keefe raised a $15M Series A in September 2025 to make 'pay with HSA/FSA' as ordinary at checkout as PayPal.