Many rumors regarding Sony Santa Monica, the developer of the God of War series, have been circulating, thanks to classified ads that have popped up looking for personnel to work on level design and art design.
Now an New Zealand retailer has posted a 28th September, 2012 release date for God of War IV, which is still unannounced. A September '12 release would be the proper development cycle for whatever Sony Santa Monica is working on, which may feature online multiplayer.