Check your Chrome user data folder. There's a decent chance a 4GB AI model is sitting there—one you never agreed to install. The file is called weights.bin, buried in a folder named OptGuideOnDeviceModel. It's the weight file for Gemini Nano, Google's on-device language model.
Delete it and Chrome downloads it again.
The same pattern has been confirmed on Windows 11, Apple Silicon Macs, and Ubuntu. Users who've been finding unexplained storage spikes for over a year now have a name for the culprit.
What it actually doesGemini Nano powers Chrome's on-device AI features: Things like "Help me write an email," scam detection, smart paste, page summarization, and AI-assisted tab grouping. On Windows, the file lands at %LOCALAPPDATA%\Google\Chrome\User Data\OptGuideOnDeviceModel\weights.bin. On Mac and Linux, it's the equivalent Chrome profile directory.
Deleting the folder provides no permanent relief. Chrome restores it on the next restart unless you disable the feature—via chrome://flags, the On-device AI toggle in Settings > System, or on Windows, a registry edit setting OptimizationGuideModelDownloading to disabled.
Chrome recently added a prominent "AI Mode" pill in the address bar. A reasonable user seeing that button—with a 4GB local model already on their disk—would assume their queries stay on-device. They don't. AI Mode routes every query to Google's cloud servers. The local Gemini Nano model doesn't power it at all.
You're paying the storage and bandwidth cost for a feature you're not actually using privately.
Is it legal or “legal”?He also drew a direct line to a case he published two weeks earlier: Anthropic's Claude Desktop silently pre-authorized browser automation across roughly three million user machines without explicit consent. It’s the same pattern, he argued, but at a much smaller scale.
The company noted the model auto-deletes if storage runs low. What Google didn't address is why users weren't asked first.
