Hanff discovered a four-gigabyte file named “weights.bin,” in a directory called “OptGuideOnDeviceModel.” The file contains weights — the learned numerical parameters of an AI model that teach it how to weigh the importance of various data points — of Google’s Gemini Nano, which is designed to live on users’ devices, not the cloud.

“Chrome did not ask,” Hanff wrote. “Chrome does not surface it. If the user deletes it, Chrome re-downloads it.”