Its not the same oil. Revision numbers are different which for mobil 1 oils indicates a different formula. The proof for that is all m1 EP viscosities have the same revision numbers, regular m1 same thing, truck and suv same thing, but x3 and x4 differ.The spectrometer analysis for X3 and X4 are practically identical, I wonder what the difference between the two is. Could it be they just decided to get SP and A40 approvals on X3, and they just released the same oil under a new label?