If you pay close attention to Sony's video about sharing video games on the PS4 then you'll likely note that playing the multiplayer portion of games on the PlayStation 4 will require a PlayStation Plus account. This was also mentioned briefly in a slide during the E3 press conference on Monday evening.
The fine print in the video notes:
"PS4 multiplayer online access requires PSN account & PS Plus subscription."
A PlayStation Plus subscription costs $17.99 for three months and $49.99 for a full year, with Sony expected to offer a one month subscription for $9.99. Besides enabling multiplayer, PlayStation Plus subscriptions offer free games, free game content, and work across all PlayStation family accounts including PS3, PS4, and PS Vita.
While this move may be disheartening to some PlayStation platform fans (because multiplayer via PlayStation Network has always been free), it is not shocking news. Microsoft has been charging for Xbox Live Gold access since the Xbox era and its subscription service - until this week - did not offer any free extras. Sony also emphasized that you do not need a Plus account to use your entertainment apps, to buy content on the Marketplace or to play single-player on any games...
Xbox Live Gold on Xbox 360 and Xbox One costs $24.99 for three months and $59.99 for a year.