Uncompressed 4k stream @ 30fps and 24bpp would be 5.7 GB/s. The top regular SD card speed, UHS-III, maxes at 0.6 GB/s. SD Express, where a PCIe lane is added, goes to 3.9 GB/s.
So, yeah, going to need at least some compression. Good news is that just a little compression can go a long way.