IPV6 API request 1x or per request

I see that we can shut off support for IPV6 via the api. I am just wondering is this a “Zone Setting” or is this a per request item setting for every user that hits the site with IPV6?

i.e 1x and its set or happens per request of user.

I would imagine that when you write the api setting and its set for the zone record? Any clear information would be greatly appreciated.