Duolingo

Duolingo is a language-learning company built around a mission of making education free and universally accessible, originally started as a Carnegie Mellon research project and going public on Nasdaq in July 2021 . Co-founder Severin Hacker describes it as "technology-first" from day one, with AI now extending that premise: the first 100 courses took roughly 12 years to develop, while AI helped add 148 new courses in just one year . The product's growth engine is a culture of relentless A/B testing—internally called the "Green Machine"—where even flagship features like the Streak system underwent over 300 iterations after their initial launch . As of late 2025, monthly active users stood at about 130 million, with 80% of growth still coming organically . The company monetizes through tiered subscriptions (Free, Super, and Max), placing newer AI features like "Video Call with Lily" in the premium tier to offset per-use API costs, while keeping the core daily learning experience free .