[Merrill]

It looks like this is not an ARM core, but a Fujitsu implementation of the Arm v8-A instruction set and Fujitsu-developed Scaleable Vector Extension. Most likely the latter is doing all the heavy lifting.

https://www.fujitsu.com/global/about/resources/news/press-re...

>A64FX is the world's first CPU to adopt the Scalable Vector Extension (SVE), an extension of Armv8-A instruction set architecture for supercomputers. Building on over 60 years' worth of Fujitsu-developed microarchitecture, this chip offers peak performance of over 2.7 TFLOPS, demonstrating superior HPC and AI performance.

[d_tr]

The text you linked to actually says that the SVE was developed cooperatively by Fujitsu and ARM, without, however, going into details about who did what.

[numpad0]

There are words floating that A64fx is basically a SPARC with ARM ISA without much ARM IP in it, no idea how accurate but intriguing