They mentioned running Linux in a VM at least twice in the keynote. I'm not sure why, unless it's an acknowledgement that OS X is no longer a usable development environment.

Linux, like any OS written in the past 30 years, is substantially architecture-independent. My day job involves coding for several devices with Linux kernels on ARM (32bit) and Aarch64 and I have no idea which is which, nor any need to.

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