AI has dramatically lowered the cost of building software, accelerating supply and intensifying competition across nearly every SaaS category. At the same time, AI-native products often carry real marginal costs, meaning free usage is no longer economically neutral. In this environment, sustainable growth is increasingly determined not by traffic volume alone, but by how effectively companies convert and expand users. Looking at the 50 fastest-growing SaaS businesses of 2025, we see clear patterns in how modern winners structure plans, gate usage, and evolve pricing. Static “good-better-best” models are giving way to more dynamic, usage-aware systems designed to fund generous freemium and drive expansion. The implication is simple: in the AI era, monetization is not a back-office function — it is a core growth capability.