Google-Extended
Google-Extended is the robots.txt token that controls whether a site is used for Gemini model training — without affecting ordinary indexing or appearance in AI Overviews.
In practice
The critical nuance: blocking Google-Extended does not exclude a site from Google’s AI responses, which draw on the regular search index. It is a principled lever on training data, not a visibility lever. Confusing it with a block on AI Overviews is the most common misconfiguration since its launch.