genius said it should exit production Feb 5. It entered production Jan 22. I think the VIN was there as soon as it entered production (status 150) but I didn't look until a couple days after. The base digits for a 2018 M3 seem to be WBS8M9C5, followed by the check digit, a J, and your 7-digit serial number. The serial number is really all you need for stuff like parts lookups, but to track your car in shipping you need the full VIN. I used
http://www.alton-moore.net/vin_calculation.html to get the check digit. It's cool, he also explains how it's calculated for geeks like me.