Google Chrome has been quietly downloading a 4GB Gemini Nano AI model onto eligible devices without directly notifying users, according to a report by privacy researcher Alexander Hanff.
The file, named weights.bin, is stored inside a folder called OptGuideOnDeviceModel within Chrome’s user data directory. Hanff discovered the behavior while conducting an automated audit on a fresh Chrome profile using macOS kernel filesystem logs.
According to the report, Chrome created a temporary directory, downloaded the AI model components, and stored the completed file on disk in about 15 minutes without any prompts or user interaction.
The same behavior was reportedly confirmed on Windows 11, Apple Silicon Macs, and Ubuntu systems. Users who previously noticed unexplained storage usage now appear to have identified the source.
Gemini Nano powers Chrome’s on-device AI tools, including email writing assistance, scam detection, smart paste, page summarization, and AI-assisted tab grouping.
On Windows systems, the file is stored in the Chrome user data folder under OptGuideOnDeviceModel\weights.bin, while Mac and Linux systems use equivalent profile directories.
Deleting the folder does not permanently remove the model. Chrome reportedly downloads it again after a restart unless users disable the feature through chrome://flags, the On-device AI setting under System preferences, or a Windows registry edit disabling OptimizationGuideModelDownloading.
The report also noted that Chrome’s “AI Mode” button in the address bar does not use the local Gemini Nano model. Instead, AI Mode sends queries to Google’s cloud servers, meaning users still consume storage space and bandwidth for a local AI model that does not handle those requests privately.
Hanff argued the behavior may violate EU privacy rules, including Article 5(3) of the ePrivacy Directive, which requires user consent before storing data on devices. He also cited GDPR provisions related to transparency and privacy by design.
Google acknowledged on its support pages that Chrome may download generative AI models in the background to support browser features. The company also said users gained the option in February to disable and remove the model through Chrome settings, preventing future downloads and updates.
Google added that the model automatically deletes itself if device storage becomes limited. However, the company did not explain why users were not asked for permission before the download began.
The report also pointed out that Google’s own Chrome developer documentation advises developers to inform users about large downloads, guidance that was reportedly not followed in this case.
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