@rsberzerker you do not need a 128-bit CPU and/or 128-bit OS to do 128-bit math 
Internally hashcat uses uint64 for pretty much everything, including keyspace. But as hardware gets faster and clusters get larger, we will need to rewrite hashcat to use uint128. It's a major change that will require a lot of work, and historically there's been little to no incentive to do this. But Sagitta HPC already has several clients who can realistically brute force keyspaces larger than 2^64 - 1, so the change will likely occur in Hashstack first and will maybe get backported to Hashcat later, and it will probably happen relatively soon.
Internally hashcat uses uint64 for pretty much everything, including keyspace. But as hardware gets faster and clusters get larger, we will need to rewrite hashcat to use uint128. It's a major change that will require a lot of work, and historically there's been little to no incentive to do this. But Sagitta HPC already has several clients who can realistically brute force keyspaces larger than 2^64 - 1, so the change will likely occur in Hashstack first and will maybe get backported to Hashcat later, and it will probably happen relatively soon.