Summarizer API asking for output language

[Yash]

The documentation on Summarizer API does not mention any information about it expecting a output language option, but on creating a Summarizer it is showing me warning that output language should be specified

Please provide what exactly should be given in initializing options to solve this.

Thank you.

[Thomas Steiner]

Hi Yash,

This information is currently indeed not covered in our docs, but I have filed a content bug for us to cover it, and meanwhile would like to point you at the relevant Explainer section that has code samples as well.

Cheers,

Tom 

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[Luca K]

Yash,

Chrome’s on-device AI APIs expect you to declare the output language everywhere you touch the model; otherwise the browser logs that warning.

My fix was to thread the language code (for example 'en', 'es', or 'ja') through both the availability check and the session creation call before you issue summarize() or rewrite():

```
const OUTPUT_LANG = 'en'; // or 'es', 'ja'

await chrome.ai.summarizer.availability({ outputLanguage: OUTPUT_LANG });
const summarizer = await chrome.ai.summarizer.create({ outputLanguage: OUTPUT_LANG });

await chrome.ai.rewriter.availability({ outputLanguage: OUTPUT_LANG });
const rewriter = await chrome.ai.rewriter.create({
  outputLanguage: OUTPUT_LANG,
  sharedContext: '…'
});

```

If you skip the language in either place, Chrome assumes “auto” and fires the warning.
Passing the same outputLanguage value in both calls and subsequent API call-satisfies the safety attestation requirement and the warning goes away.

[Thomas Steiner]

Yes, this exactly is the behavior we strive to document. For now, the fallback of the API is to just assume English, but of course in the long-term this is not a behavior we want to hard-wire. Eventually , ifit is not known, the API is rather to throw than to assume English. 

Thomas Steiner, PhD—Developer Relations Engineer (blog.tomayac.com, toot.cafe/@tomayac)

Google Spain, S.L.U.

Torre Picasso, Pl. Pablo Ruiz Picasso, 1, Tetuán, 28020 Madrid, Spain

CIF: B63272603

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[Ken Kahn]

Why can't the default be derived from Chrome's language settings?

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[Thomas Steiner]

On Fri, Oct 17, 2025, 08:14 Ken Kahn <toon...@gmail.com> wrote:

Why can't the default be derived from Chrome's language settings?

This would make testing a nightmare as you can't know what languages your users have set in their preferences. The current assumed default of English also isn't great given eventually this API shall work with many languages, so the spec and the implementation encourage the setting of the languages explicitly, and in the long-term calls might even fail if no languages are present in the options. 

[Die4Ever2005]

"the spec and the implementation encourage the setting of the languages explicitly"

It would be a bit hard to present the user with a list of languages to choose from if we can't poll to ask the API all the languages that are supported. I know you can make 1 availability call per language, but that requires me to know all the languages that could be supported. I guess ideally there'd be a call to get a list of language codes with full names.

[Thomas Steiner]

Getting the list of supported languages came up in a similar context before. @Kenji Baheux, @Etienne Noël, should we re-open this Issue? I think having a way to explicitly query the supported input and output languages makes sense, especially since developers need to (but also can) hard-probe all language combinations, so a more convenient method sounds justified.  

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[Etienne Noël]

+chrome-chia-dev 

I'm not against it. Do you see a specific method or just as part of availability?