There's been lots of buzz about SP4-M lately due to the apparent price hike of the OEM products. In my area, 6 local dealers (Jeep,Kia, Hyundai) use what JustN89 stated (BG) even on vehicles still under warranty . This goes against what skyactive claims about dealers insisting by-the-book OEM fluids only.
To the OP, dig around a bit and you will find about a dozen products that list "compatible with" SP4-M. Even the Warren MAG 1 product claims SP4-M compatibility. What's odd is that the Asian and European brands (Eneos, etc,) have not changed their labeling from SP4 to SP4-M. Something I "imagined" that I read somewhere was that the U.S. version initially came out as a synthetic blend and the M version is now full synthetic, just like the Asian and European brands have always been. Just my thought that I wish someone would try to disprove.
Battles rage on Hyundai and Kia forums that their trannies are especially sensitive to fluid and the use of a universal product is hotly contested. LOTS of evidence shows up at BITOG to suggest people are getting very long life using non OEM fluids.