Chrome Silently Installed a 4 GB AI Model on My PC
I found a hidden 4 GB weights.bin file in my Chrome profile. Here is what it is, why it keeps coming back if you delete it, and how to actually stop it.
I noticed it on a Saturday morning while running a routine cleanup.
My SSD had been complaining about space for weeks. I cleared old node_modules folders, blew away dead Docker images, emptied the trash. Nothing moved the needle the way I expected.
So I opened a disk-usage scanner and let it walk the whole drive.
The first surprise was that Chrome was sitting at over 5 GB. Not the install. The user profile.
The second surprise was a single file inside it called weights.bin, weighing in at almost exactly 4 GB.
I had not asked for a 4 GB file. I had not been told a 4 GB file existed. And the name looked an awful lot like an AI model.
This is what I found when I started pulling the thread.
Where the file lives
On Windows, the path is buried where most people will never look:
C:\Users\<your-name>\AppData\Local\Google\Chrome\User Data\OptGuideOnDeviceModel
On macOS, the same idea sits at ~/Library/Application Support/Google/Chrome/OptGuideOnDeviceModel. On Linux it is at ~/.config/google-chrome/OptGuideOnDeviceModel.
Inside the folder is a versioned subdirectory and one large weights.bin file. There is no readme. There is no setup wizard that mentioned it. There is no settings page in Chrome that says “you have a 4 GB model installed and here is how to remove it” the way a Steam library lists installed games.
It is just there.
What the file actually is
The bin is the model weights for Gemini Nano. That is Google’s small on-device language model, the kind designed to run inside the browser process without calling out to a cloud endpoint.
Chrome uses it to back a handful of features. The “Help me write” prompt that appears in text fields. On-device scam and phishing detection. Smart paste. Page summaries. AI-assisted tab grouping. Anything exposed through the new Prompt API and the related Writer, Rewriter, and Summarizer APIs that Chrome has been rolling out for web developers.
In isolation, those features are fine. Some of them are even useful. The problem is not the existence of an on-device model. The problem is how it got onto my machine.
What triggers the download
Chrome runs a quiet eligibility check on startup. If your machine clears all four of these bars, the download begins in the background.
More than 4 GB of GPU VRAM.
At least 16 GB of system RAM.
Four or more CPU cores.
At least 22 GB of free storage on the drive holding your Chrome profile.
If you sit above all four, Chrome calls Google’s optimization-guide endpoint, pulls the model, and writes it to disk. No prompt. No notification banner. No “do you want this?” dialog. The internal feature flag that controls it, OnDeviceModelBackgroundDownload, is being switched on for eligible users before the matching toggle is even visible in your settings.
If your free disk space later drops below 10 GB, Chrome quietly cleans the model up. If you fail the eligibility check for 30 days in a row, same thing. The browser is silently managing a multi-gigabyte asset on your machine and not telling you about any of it.
What “delete it” actually does
My first instinct was to nuke the file. I closed Chrome, deleted the entire OptGuideOnDeviceModel folder, restarted the browser, and watched my disk usage drop by 4 GB.
For about a day.
The next time I left Chrome running long enough for an idle window, the folder reappeared and the bin came back with it. The eligibility checker had run again, decided I was still a good candidate, and the optimization-guide service had repulled the model from scratch.
This is the part most people miss when they first find the file. The folder is not garbage left behind by a one-time event. It is actively maintained. The browser will undo your cleanup as a matter of design.
The real way to stop it
There are two paths that actually hold up.
The settings path is the friendly one. Open Chrome and go to chrome://settings/ai. Turn off the on-device AI features there. Then close Chrome, delete the OptGuideOnDeviceModel folder one more time, and reopen the browser. With the feature off, the model does not come back.
The policy path is the hard kill. On Windows, open regedit, navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome, and create a new DWORD value called GenAILocalFoundationalModelSettings. Set it to 1. That is the official enterprise policy for blocking the local foundation model. Restart Chrome and visit chrome://policy to verify it is loaded.
I went with the policy route because I do not want to find out in six months that a future Chrome update flipped the settings toggle back on by default.
On macOS, the equivalent is a defaults write com.google.Chrome GenAILocalFoundationalModelSettings -integer 1 command. On Linux, it is a JSON file dropped into /etc/opt/chrome/policies/managed/ with the same key.
Why this bothers me more than it should
I am not against on-device AI. I would rather have a model running locally than have my keystrokes shipped to a server every time I write a sentence in a text area.
What bothers me is the consent model.
Four gigabytes is not a rounding error. It is a Steam game. It is a Linux distro and a backup, sitting in the same disk allocation. On a 256 GB laptop, it is over 1.5% of the entire drive. At a billion-device scale, it is petabytes of storage and a real amount of bandwidth, paid for by users who never agreed to host any of it.
A browser is supposed to be the layer I trust to not surprise me. The implicit contract is that it loads pages, stores cookies, and gets out of the way. Background-downloading a multi-gigabyte model into a hidden folder breaks that contract, even when the model itself is harmless.
The fix Google has shipped, the AI settings toggle, only works if you know the model is there in the first place. Most people will never check.
Where to start
If you use Chrome on a machine that meets the spec, do this today.
Open chrome://settings/ai and read what is on. Turn off anything you do not actively use. The “Help me write” entry is the one most people want gone.
Then open the OptGuideOnDeviceModel folder for your platform and check the size. If you see a multi-gigabyte weights.bin file you did not ask for, you now know what it is and what to do about it.
If you are on a managed device, or you want a permanent block that survives Chrome updates, set the GenAILocalFoundationalModelSettings policy to 1 using the registry on Windows or the defaults command on macOS. That is the one setting Chrome respects across versions.
The model is not malware. It is not stealing your data. But it is a 4 GB decision that someone else made for you, and you get to decide whether you want to keep it.