If its fairlife Chocolate, the ingrediants are:
REDUCED FAT ULTRA-FILTERED MILK, SUGAR, LESS THAN 1% OFALKALIZED COCOA, NATURAL FLAVOR, LACTASE ENZYME, ACESULFAME POTASSIUM, CARRAGEENAN, SUCRALOSE, VITAMIN A PALMITATE, VITAMIN D3

For fairlife whole milk, the ingrediants are:
Ultra-Filtered Milk, Lactase Enzyme, Vitamin A Palmitate, Vitamin D3.

No preservatives, it is the combination of ultra-filter milk that removes more of the sugars combined with ultra-pasteurization that kills more bacteria along with aseptic packaging to give it a long shelf life.


https://fairlife.com/frequently-asked-questions/#faq-how-is-fairlife-milk-produced-and-what-is-the-ultra-filtration-process

FWIW, fairlife chocolate milk is one of the richest tasting chocolate milks out their and does not last long in our household.