PlayStation 4 owners will need to subscribe to PlayStation Plus to play online multiplayer.
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This was confirmed in an official Sony video, in which it notes in small print: "PS4 multi-player online access requires PSN account & PS Plus subscription".
Multiplayer gaming on PS3 is free to access, and is widely considered one of the most attractive components of the console over Xbox 360, which requires users to pay for Xbox Live Gold access to play games online.
The video shows Sony's Shuhei Yoshida demonstrating that sharing a disc-based game on PS4 is as simple as passing the disc to another PS4 owner - in a clear dig at Microsoft's DRM-heavy used game policies for Xbox One.
However the video also notes that "the foregoing instructional video applies only to disc based games," indicating that digitally-downloaded games may be subject to DRM restrictions, as is the case on PS3.
During its E3 press conference today, Sony boasted that PlayStation 4 will not enforce any restrictions on pre-owned games or require an always-on internet connection.