I'm not aware of any new AHCI m.2 drives being produced by Samsung. The entire line up is NVME now.ACHI drives will boot like SM951's, and samsung is creating an faster SM961 drives and as long as you get it the drive as ACHI it'll work.
Btw I'm the first person who ever installed SM951 in a Mac - 3 of them in a RAID in a Mac Pro over a year ago.