Snorkel AI, a startup that helps AI labs and corporations build training data sets and simulated environments, has raised a $350 million Series E at a $3.5 billion valuation. The round, led by Insight Partners and S32, values the seven-year-old company at nearly triple the $1.3 billion valuation from its $100 million Series D 17 months earlier. Existing investors including Addition, Lightspeed, Greylock, GV, and Wells Fargo also participated.

The company originally provided software for data labeling automation, but shifted last year to a data-as-a-service model, delivering completed data sets to customers. Rather than operating purely as a human expert marketplace, Snorkel uses a hybrid approach: its software and models generate data synthetically alongside subject matter experts. Snorkel reports its annualized revenue run-rate now stands at $375 million, an 18-fold increase over the last 12 months, fueled by what it describes as AI labs’ insatiable appetite for high-end training data.

Other data companies positioning themselves as AI data labs have seen similar growth. Mercor’s gross annualized revenue has climbed to $2 billion, Handshake hit the $1 billion milestone earlier this year, and TechCrunch reported that Micro1 has scaled to $500 million. Because these companies pay roughly 60% to 70% of their top-line income directly to the domain specialists doing the work, their actual net annual revenue is substantially lower than those headline gross figures. Snorkel sells reinforcement learning (RL) environments and complete datasets rather than human labor, so payments to its human experts are accounted for in its cost of goods sold rather than in headline-generating annualized revenue numbers, according to the company.

Snorkel launched commercially in 2019 after four years of research led by co-founder and CEO Alex Ratner and his team at a Stanford AI lab.