Issue with downloadprogress event resetting to 0% on page refresh for LanguageModel.create()

[Alan Corn]

Hi everyone,

I have noticed an issue regarding the download progress monitoring of the on-device LanguageModel.

I need to display a download progress bar on my page. However, when I use the following code to monitor the download progress, the value retrieved from e.loaded always restarts calculation from 0. This means that if the page is refreshed, the download progress resets to 0, which is confusing for users.

I verified the actual status by checking chrome://on-device-internals/ > Model Status. It clearly shows that the actual download progress is not 0% (provided the browser process is not closed).

Code Snippet:

```javascript

await LanguageModel.create({
    monitor: (m) => {
        m.addEventListener('downloadprogress', (e) => {
            console.log(`DownloadProgress: ${parseFloat((e.loaded * 100).toFixed(2))} %`);
        });
    },
    expectedInputs: [
        { type: 'text', languages: ['en'] }
    ],
});

```

Environment:
Browser Version: Chrome 144+

Steps to Reproduce:

1. Execute the script above in the console.
2. Observe that the progress starts printing from 0%.
3. When the download progress reaches 5%, open a new tab, open the console, and execute the same script.

Expected Result:
In the new tab, the download progress should reflect the actual status (e.g., starting from 5%).

Actual Result:

1. In the new tab, the download progress resets and starts printing from 0%.
2. After reaching approximately 95%, it pauses for a moment and then jumps directly to 100%.

Has anyone else encountered this behavior? Any insights would be appreciated.

Thanks!

[Thomas Steiner]

Hi Alan,

This is actually working as intended. Each tab reports its 0 to 1 progress based on what has already been downloaded. Let's assume a 1GB model. You open tab1 and the model downloads 250MB, so tab1's download progress is at 0.25. Then you open tab2, and we have 750MB left to download. But rather than starting at the absolutely correct value of 0.25, tab2's download progress again starts at 0, but reaching 1 is now only 750MB away. We do it this way to prevent malicious sites from matching users on different sites by monitoring their model download progress. 

Cheers,

Tom

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[Alan Corn]

 Appreciate the explanation. Thank you very much!