384
Former Intel CPU engineer details how internal x86-64 efforts were suppressed prior to AMD64's success
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
AMD64 is the name of the instruction set they program to, it has nothing to do with how many bit the CPU is. Obviously the core instruction set is 64 bit, but as I've tried to explain, a chips bit width is not realistically determined by instruction set alone anymore.
Although they are almost identical, the equivalent Intel to AMD64 is called i64.
AArch64 Is the Arm Architecture family 64, again the instruction set you program for, and not the bit width of the CPU.
None of those describe the address bus width either. i64 and AMD64 and AARCH64 come will all sorts of different address bus widths, all of which are less than 64 bit wide.
https://www.tomshardware.com/reviews/processor-cpu-apu-specifications-upgrade,3566-2.html
Although this is a bit dated, the latest I heard was 48 bit address bus, which would surpass the above from 2013 by a factor of 256.
Obviously none of these 64 bit architecture CPU's are called neither 40 or 48 bit.