Google-Extended: what it is and whether to allow it

A Google token, not a crawler: it controls whether content already crawled by Google is used for Gemini and Vertex AI training.

Test whether you are blocking it

curl -sS -A "Google-Extended/1.0" -o /dev/null -w "%{http_code} %{size_download}\n" https://example.com/

A 403 means a firewall or bot rule matched. A tiny body with status 200 means the crawler reached a shell or a challenge page and read nothing useful. Both are failures; they just look different.

Should you allow it

It appears as a robots.txt token rather than a user agent in most logs, so blocking it does not affect Google Search indexing at all — a frequent misunderstanding that leads to alarm.

Where this fits

Crawler access is check A1 of the fifteen-point audit, and it comes first: nothing downstream matters if the request is refused. The full list is in the standard; the sequence that avoids redoing work is in the repair guide.