GPTZero, the three-year-old AI detection startup that Princeton grad Edward Tian first built as a senior thesis project, has been acquired by Superhuman, the companies announced on Tuesday.

Terms of the deal were not disclosed, though Tian told Business Insider that GPTZero amassed more than 19 million registered users and $30 million in annual recurring revenue.

In 2024, Tian told TechCrunch that it was profitable. Tian and co-founder CTO Alex Cui, who’d been friends since high school, raised a $3.5 million seed round led by Uncork Capital, followed by a $10 million Series A in June 2024 led by Footwork co-founder Nikhil Basu Trivedi, with several other notable investors including Reach Capital, Jack Altman’s Alt Capital, and Neo. All told, the company raised just $13.5 million.

Superhuman — the company formed when Grammarly bought email provider Superhuman last year and rebranded under that name — already had an AI detection tool built into its platform. GPTZero’s mission has been to help humans detect and defend against AI slop. Grammarly’s tool has been designed to help users, often students, determine whether their writing appears AI-generated, then revise it so it doesn’t. As for why Superhuman bought a competitor, Superhuman says that “two AI detectors are better than one.”