The Nikon Z 9 only supports CFexpress memory cards of type B as well as the predecessor XQD 2.0. The option to also use XQD cards, contrary to the current industry trend, should primarily be understood as a customer service, since Nikon was one of few camera manufacturers to rely on XQD early on and the one or other XQD 2.0 card might be in the camera bag of photographers. However, we strongly recommend to buy CFexpress cards.
Statements about the requirements for 8K RAW video recording cannot yet be made at the time of testing, but a constant data stream of over 500 MB/s can be expected. Thus, the fastest models should be just good enough.
Fast memory cards also do not hurt for fast continuous shooting: Nikon gives the Z 9 a tiny image buffer that can hold just 21 pictures in the highest quality settings. Or pretty much exactly one second of continuous shooting. After that, 600 MB/s and more can easily accumulate when shooting at 20 frames/s in RAW quality. Only the fastest models in the test can guarantee (almost) uninterrupted burst shooting.