YandexAdditional
YandexAdditional is a robots.txt control from Yandex, not a separate crawler. It controls whether Yandex may show your pages in its AI responses.
What it does
Yandex fetches pages with YandexBot and checks the YandexAdditional group in your robots.txt to decide how it may use them. Blocking YandexAdditional does not stop YandexBot crawling your site.
Model training and content-use controls. Some also govern answer grounding; review the operator's policy before changing access.
robots.txt
To block YandexAdditional, add this to the robots.txt at the root of your site:
User-agent: YandexAdditional
Disallow: /
User-agent: YandexAdditionalBot
Disallow: /Blocking it asks the operator not to use your pages for model training from then on. It does not remove content already collected, and it does not stop the operator's search crawler or live fetchers, which use their own user agents.
To allow it explicitly, for example after a broader rule blocks other crawlers:
User-agent: YandexAdditional
Allow: /
User-agent: YandexAdditionalBot
Allow: /Check what your robots.txt allows for YandexAdditional and the other AI crawlers in this directory.
In SurfacedBy
YandexAdditional never appears in a request, so there is no traffic to count. SurfacedBy's robots.txt checks report whether your site allows it, alongside YandexBot, which makes the requests.
Operator documentation
Details on this page come from Yandex's own documentation: yandex.com/support/webmaster/en/robot-workings/check-yandex-robots.