Grammarly parent Superhuman buys AI detector GPTZero

Superhuman Inc., the company formerly known as Grammarly, said today it has agreed to acquire GPTZero Inc., the startup whose detection tools tell teachers, editors and hiring managers when a piece of writing came from a machine.

The acquisition price was not disclosed.

The acquisition is arguably ironic. Grammarly spent years building tools that help people write with artificial intelligence. Now, under its new Superhuman name, it is buying the company best known for catching that same AI output. The rebrand in October came as Grammarly pushed past grammar correction into a wider productivity platform.

Superhuman calls the purchase part of an authenticity layer, its term for tools that show where content came from and whether to trust it. GPTZero will be built into Superhuman Go, the company’s AI assistant, which Superhuman says works across 1 million apps and websites.

GPTZero was launched in 2022 and was one of the first AI writing detectors to take off after the arrival of ChatGPT the same year. The company says it now has 19 million registered users and around $30 million in annual recurring revenue. Founders Edward Tian, Alex Cui and about 30 staff are moving to Superhuman.

Detection is no longer the whole product. GPTZero also flags fake citations and made-up statistics, checks for plagiarism, verifies that cited sources exist and scans social feeds for AI content through a tool called AI Vision that launched in February. A separate feature, Replay, logs the keystroke history of a document to show how it was actually written.

Superhuman is not arriving empty-handed. Its own detector, kept from the Grammarly days, ranks first for quality on RAID, an independent benchmark that runs detectors against more than 670,000 samples. Two detectors trained on different data, the company argues, catch more than one.

“Together, we’re bringing the most trusted writing tool and the most trusted AI detector into one platform, so that confidence in content becomes the default for writers and consumers,” Superhuman Chief Executive Shishir Mehrotra said in a statement.

The timing tracks a real shift. A Graphite study cited by Superhuman found AI now writes about half of all newly published online articles. Detectors started in the classroom and have since moved into hiring, publishing and compliance work. They are also still wrong often enough to produce false positives.

Coming into its acquisition, GPTZero had raised approximately $13.5 million in venture funding, including a $10 million Series A in June 2024. PitchBook last valued the company above $88 million.

Superhuman started in 2009 in San Francisco and now claims 40 million daily users.

Image: GPTZero