AMD's Zen 4 microarchitecture is currently under development
At its Next Horizon Event earlier this week, AMD officially said that it had started working on the Zen 4 microarchitecture. It did not disclose anything else so we can only speculate as to what it could be.
The present Zen 2 microarchitecture is already being sampled and CPUs made with Zen 2 such as the EPYC Rome are 7 nm parts fabricated using TSMC's first generation N7 technology. Zen 2's successor, Zen 3, will continue to be a 7 nm part and will be made using TSMC's N7+ technology that will employ EUV lithography. So that leaves us wondering as to what could be Zen 4's manufacturing process. We can speculate 5 nm, but that would be just a wild guess at this point.
The Zen 3 parts are expected to start shipping in 2020, which means we will be seeing AMD sticking with 7 nm for at least the next two years. Zen 4 could start shipping in 2021 or even later. What would be the likely benefits of Zen 4 you ask? The same as with any processor generation — higher performance per watt than previous generations.
It remains to be seen what AMD has in store for Zen 3 and beyond. We are currently in the Zen+ stage, which is an optimization phase in AMD's inflection-optimization cycle. Thus, upcoming inflection phases are Zen 2 and Zen 4, with Zen 3 more likely to be a Zen 2+ than a major architecture revision.