Looks like it's Group 3. Damn.
"Base Stock is the material that oil starts from - petroleum-based or true synthetic. All oil is classified under one of five Groups, I-V. Groups IV and V are full synthetic and have no petroleum base. They use synthetics that are more resistant to heat and stress than petroleum-based oil. High Performance and Racing oil are almost always Group IV or V.
Groups I, II, III are all petroleum-based with III being the highest quality. All BMW-approved oils are Group III yet are still marketed as synthetic oils. This is to avoid confusion with the different base stocks of Group IV (PAO) and V (ester). Any oil brand that wishes to be approved by BMW must be a Group III base stock. So it's common to see premium high performance oil that is better than BMW oil but does not have BMW approval. Red Line Oil encountered this with their own High Performance oil that could not be BMW approved due to their Group IV and V base stock. They had to formulate a different oil with a Group III base to get the BMW approval (Red Line Professional Series). This oil actually performs worse than their High Performance oil in laboratory tests but carries the BMW stamp of approval."
https://www.bimmerworld.com/BMW-Engine-Oil/