Heirloom develops direct air capture technology that accelerates limestone's natural carbon mineralization process from years to days, producing a pure CO2 gas stream for permanent underground storage and reusable calcium oxide powder in a closed-loop system powered by renewable energy. The company operates America's first commercial DAC facility in Tracy, California, with plans for two facilities in Shreveport, Louisiana, targeting a combined annual CO2 capture capacity of 320,000 tons. Customers include Microsoft, which signed a deal for 315,000 metric tons of CO2 removal; Stripe, Meta, JP Morgan, McKinsey, Shopify, and H&M Group. Heirloom raised $150 million in a Series B funding round to scale its DAC technology. It maintains a prototype facility in Brisbane, California, and was founded in 2020 in San Francisco. CEO Shashank Samala leads the company, which partners with Leilac for electric kiln technology.