Exactly what qualifies for you may mean it does already exist on a large scale or doesn't.
Alaska's UBI program gave 1.3k this year, which I'm guessing many commenters here would say is too small to be a real UBI, but it is universal and has been going for almost 50 years
I wouldn't call the permanent fund a UBI. It's proceeds from the sale of oil, whereas every other UBI requires some taxation, wealth transfer, or cuts in spending elsewhere.
Because Alaska is unique, AFAIK the only state in America that sells something. Everything else is income redistribution. The money has to come from somewhere. It's a very fine line, I agree, but the permanent fund only exists because the state can generate that income from something other than increased taxes, redistribution, or reducing spending some place else.