Google Chrome has been quietly downloading and installing a 4GB Gemini Nano AI model on user devices without displaying a consent prompt or offering a clear opt-out mechanism.
The findings were published by privacy researcher Alexander Hanff of That Privacy Guy, who documented the behavior through filesystem-level analysis on macOS and corroborated it with Chrome configuration data, updater logs, and feature flags. Additional user reports suggest the behavior is also affecting Windows and Linux systems.
Auto-downloading Gemini Nano
According to Hanff, the AI model is installed in a directory named OptGuideOnDeviceModel within the Chrome user profile. The file, identified as Gemini Nano’s model weights, powers several local AI capabilities integrated into Chrome, including “Help me write,” on-device scam detection, smart paste, page summarization, and AI-assisted tab grouping.
Hanff said he discovered the behavior while running an automated privacy audit using a fresh Chrome profile on an Apple Silicon Mac. Using macOS .fseventsd logging service, he traced the exact sequence of events showing Chrome creating temporary unpacking directories, downloading model components, and eventually placing a large weights.bin file into the browser profile.
Filesystem logs show the installation process took roughly 14 minutes and included additional optimization-guide components alongside the Gemini Nano weights.
Chrome’s internal feature flags allegedly revealed that the browser enables “OnDeviceModelBackgroundDownload” before exposing corresponding AI settings to users, meaning the model can be downloaded before users even see the controls associated with it.
Gemini Nano is Google’s lightweight on-device large language model designed to run AI tasks locally instead of sending prompts to cloud servers. Google has increasingly integrated Nano into Chrome as part of its broader Gemini AI rollout.
Chrome currently uses Gemini Nano for several optional AI-powered features, though it should be pointed out that the browser’s highly visible “AI Mode” interface remains cloud-backed and still sends user queries to Google servers rather than using the local model.
Hanff argues the behavior may violate European privacy rules, including the ePrivacy Directive and GDPR transparency requirements, because information is stored on user devices without explicit prior consent.
The researcher also questions whether the deployment could attract scrutiny under the EU Digital Markets Act, which imposes obligations on dominant technology platforms regarding defaults and user choice.
How to stop this
Multiple users have reported that manually deleting the weights.bin file does not permanently remove it. According to the investigation, Chrome eventually restores the model during later updates or eligibility checks unless the AI download mechanism is explicitly disabled.
The file is commonly stored in the following locations:
- Windows – %LOCALAPPDATA%\Google\Chrome\User Data\OptGuideOnDeviceModel\
- Linux/macOS – ~/.config/google-chrome/OptGuideOnDeviceModel/
Users who want to stop Chrome from downloading the model currently have limited options.
On Chrome 137 and newer:
- Open ‘chrome://flags'
- Search for ‘optimization guide on device'
- Set the feature to ‘Disabled'
- Restart Chrome
On Windows systems, administrators can also disable the behavior through Group Policy or by creating the following registry policy on:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome- Create a DWORD value named ‘OptimizationGuideModelDownloading'
- Set its value to ‘0'
After disabling the feature, users can manually remove the OptGuideOnDeviceModel directory to reclaim disk space.
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