PS Plus membership required.
Here are the details from James Hallahan of PlayStation Plus, to quote:
"We’re back with another free multiplayer weekend on PS4, but this time, the PS Plus team is extending it a full week. That’s right — one full week of competitive or cooperative play online! This should give you enough time to prestige at least once on Call of Duty: Infinite Warfare, right?
Starting this Friday, February 17, you, your friends, your next door neighbor — everyone — will be able to access the online multiplayer modes in any PS4 game that you own without a PlayStation Plus subscription.
Free online multiplayer access begins February 17 at 12:01 AM Pacific and runs to Sunday, February 23 at 11:59 PM Pacific. Hop on to PSN during the free week with your favorite multiplayer game — no membership commitment is required during this period. Enjoy!"