Please find below, Update 10 release notes. This Update bring Offline play to SimCity.
SimCity Single-Player Mode.
o Enables Offline Play.
o Single-Player Mode includes multi-city play, regional interdependence, and city specialization. Regions are saved locally and there is no limit on number of save games.
o Autosave can be disabled in Single-Player Mode in order for players to experiment and load their regions at a previous save point.
o Save As a copy feature. Players can make copies of their regions at multiple save points.
o See FAQ on Single-Player Mode for full details. http://help.ea.com/en/article/simcity-single-player-mode-faq/
Optimizations in the simulator to improve performance of both Multiplayer and Single-Player Mode.
Friends Search now uses the Origin friend search.