Ads.txt
en.wikipedia.org
en.wikipedia.org
Suppose someone wants to run a service that will put your ads on all the popular sites, one stop shopping. Facebook only sells ad space directly, but this company would simply take your money and use it to buy ads from Facebook and others, which is totally legitimate. And Facebook interfering with this would have obvious anti-trust implications.
# Facebook.com/ads.txt
#
# Facebook inventory can only be purchased from Facebook advertising
# systems, and cannot be purchased programmatically through open
# exchanges. Therefore there are no authorized sellers or resellers
# listed in this facebook.com/ads.txt file.
https://www.facebook.com/ads.txtThat would require knowing all the user agents that would scrape content, assuming that you want to only exclude AI scrapers and not search engines in general.
OpenAI's user agent is GPTBot[1], I am not sure about the others.
There is still a difference between scraping content for the purpose of searching it and training on it.