I ran across the AWS re:Invent video from the session put on by AMD to promote the Epyc and Radeon stuff that AWS is offering. As an aside, the video had 89 views as of the time I was writing this so it's definitely not a hot topic. Note this was done in December, so not about the stuff just announced.
AMD Epyc instances are offered at a 10% discount from Intel instances. Since they were launched last year, AWS has been offering them in the T, M, and R lines (burstable, balanced, and memory weighted). This year they are offering some "semi-custom" processors in the C line (compute weighted) with faster processors than you can get elsewhere, so apparently AWS is buying that yield instead of Apple.
Notably missing from the AMD offerings on AWS is anything in the X line (extreme memory weighted). The most memory in an AMD offering is 768 GiB. The X line goes up to 3,904 GiB, all Intel.
I'll be keeping an eye out for any announcements about the new stuff going into any AMD instances, but it is interesting that AMD had to sponsor a session to tell a crowd notorious for jumping on any cost optimization that they could save 10% on their EC2 bill by tacking an "a" on the end of the instance type.
Are you guaranteed to get Intel if you are not running a ***a instance or they might give you the AMD instance?