While I know it does exist BigInteger sometimes it would be needed to have a type that is explicit 128 bit and nothing more probably it would be more efficient too (at least in a 64 bit machine at it could be represented as a couple of longs).

An Int128 is the "natural" type of GUID, IP6 addresses and more at low level but nevertheless true x86 instruction CPUID returns 4 integers (in 4 registers) that need to be "concatenated" to get the real value, the real "intent" was to return an Int128.

I have doubt if an "alias" could exist if a long is an abbreviation of "longword" and Int128 could be octa as abbreviation of "octaword"? The literal at that point could be "O" or "o"...