Google-Extended does not affect AI Overviews — it controls whether your content is used to train Google's generative AI models, while AI Overviews eligibility is governed by standard Googlebot indexing and the same content and structured-data guidelines that apply to classic Search.
Google announced Google-Extended in a September 2023 blog post as a training-opt-out control. The subsequent AI-features documentation reinforces the separation: AI Overviews use the standard web index, so blocking Googlebot removes you from both classic Search and AI Overviews, while blocking Google-Extended only opts you out of training.
Publishers who want to appear in AI Overviews but not contribute to model training can safely deploy User-agent: Google-Extended / Disallow: / alongside their normal Googlebot policy.
The one gotcha: Google-Extended's scope is documented as covering Gemini apps and Vertex AI generative APIs, not the AI Overviews surface itself. If Google broadens the scope in future documentation, revisit the policy.
For most publishers the training-versus-appearance split is a reasonable middle ground: retain search and AI Overviews visibility, decline to be pretraining data.