Google-Extended is a standalone product token in robots.txt that tells Google whether it may use your content for Gemini training and grounding, according to Google’s list of common crawlers. It has no crawler of its own: Google crawls with its existing user agents and only uses the token as a setting.
The token controls whether your content may be used to train future Gemini models that power the Gemini apps and the Vertex AI API for Gemini, and for grounding in the Gemini apps and Grounding with Google Search on Vertex AI.
What does it not control?
Google writes that Google-Extended does not affect a site’s inclusion in Google Search and is not a ranking signal. AI Overviews and AI Mode are part of Google Search too. According to AI features and your website, you control what appears there with the robots.txt rules for Googlebot and with nosnippet, data-nosnippet, max-snippet or noindex.
Example
User-agent: Google-Extended
Disallow: /This signals that your content may not be used for Gemini training and grounding in the products mentioned. You remain findable in Google Search as before.
Common mistake
Looking for Google-Extended in your server logs. Because the token has no user agent of its own, you will never see it there. You only see the regular Google crawlers.