Google-Extended is a product token that lets you control certain AI uses by Google in robots.txt. It is not a separate HTTP user agent and is not the same as Googlebot.
Google-Extended lets website owners control certain AI uses by Google without affecting classic Google Search. Google explains that is not a separate ; crawling happens via existing Google user agents, while Google-Extended is used in as a product token.
The most common mistake is confusing it with :
User-agent: Google-Extended / Disallow: / controls only AI use,
User-agent: Googlebot / Disallow: / endangers classic Google visibility.
So if you want to restrict Google AI use, do not accidentally block Googlebot. The two tokens serve different purposes and must be handled separately and deliberately.