Most of this is over my head, but what I understand of it is rather concerning. I have never installed the Chrome browser and generally avoid using Google if at all possible, but I thought you folks might want to know about this, even if it turns out to not be a big problem.
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Another reason to steer clear of Chrome!
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You can turn it off via Chrome > Settings > System > On-device AI.
Google explains that it is used to “perform AI-powered tasks”, which currently may include:
- Help with writing or rephrasing text
- Warn you about scams
- Summarize web pages
- Organize your tabs
But I think this is the direction software is going. At first it will be for optional services, but someday it will be mandatory. It’s like how these days software assumes you have an always-on Internet connection.
I asked Claude to plot growth of software size for Mac applications:
Note that this is log scale, so it is deceptively flat!
I’ve read that the proper way to turn this off in Chrome for MacOS is open chrome://flags and search for “Enable Optimization Guide” (I’ve read that the rest would read on Android, but mine said on Device - a direct flag link would be chrome://flags/#optimization-guide-on-device-model) and disable that setting, restart Chrome, and then you can delete the downloaded model file (about 4 GB; I believe I found it in the library folder in my home folder, so ~/Library/Application Support/Google/Chrome and I believe it was a file called “weights.bin” in a folder called “OptGuideOnDeviceModel”.)
I don’t use Chrome much, but since disabling that chrome flag and deleting the downloaded file, it has not come back.
[edit] Note that the above does not work. Apparently the only thing that does is to go into Chrome Settings, click “System”, and turn off “On Device AI”, which Google says is “rolling out” 
- my Chrome settings do not have that setting yet. So I’m keeping the model downloaded for now, and I’ll continue to use Chrome only when Safari or Firefox aren’t as good.
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Here is a summarized version of the report in the OP (original post) :
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More from Ars Technica:
Just this week, someone noticed that Chrome had downloaded a 4GB Gemini Nano model and inferred from its sudden appearance that Google was deploying that AI on all Chrome installs right now. That’s not exactly true. Google announced in 2024 that it would begin adding local AI capabilities to Chrome, powering features like Help Me Write, tab organization, and scam detection.
The list of potential uses has changed over time, and Google never rolled the models out universally. It’s possible your machine has been running a local Gemini Nano model since 2024, and it’s also possible the AI was downloaded yesterday. Google tells Ars Technica the flags that determine whether or not Gemini Nano is installed on your machine are multifaceted and include (but are not limited to) your computer’s hardware, account features, and whether you’ve visited a website that uses Google’s on-device Gemini API.
Because Gemini Nano is constantly appearing on machines for the first time, people may think this is something new. In reality, Google confirmed to Ars that Chrome’s Gemini Nano model has been around 4GB in size since it debuted two years ago.
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… And to be fair, running AI models locally is not much different from Apple running their AI models locally - which is done in a wide variety of contexts.
Do I trust Google to not use this AI to capture my private data? No, I don’t. But nothing has changed with respect to privacy - Chrome has been abusing user privacy long before they added a Gemini model to it.
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