Question about ASUS TUF Gaming GeForce RTX 4070 Ti SUPER OC

Hello, I would like to know what the difference is between the Asus TUF-RTX4070TIS-O16G-GAMING (870 CHF) and the Asus TUF-RTX4070TIS-16G-GAMING. What does the O in "O-16-G" stand for, and which would be the better choice?