At vultr you have the option to "bring your own ip", as they call it. This really just allows you to use BGP to announce whatever prefixes you own. You could have a /40 behind each of your servers if you wanted to.
Which is great to have as an option--but otherwise, it's a stupid idea. The whole point of having such a large address space with IPv6 is to enable aggregation of routes. So, every vultr datacenter should have at most one route in the global IPv6 routing table, for a huge prefix that all their customers are aggregated under. Having customers announce their own provider independent address space might well have its legitimate uses, but it adds additional routing table entries to the global routing table, which is why it's a terrible idea to do this instead of just assigning customers /48s from their provider aggregated space.