iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
New iMac Unboxing Video and Teardown Photos
Meanwhile, Japanese site Kodawarisan has posted teardown photos showing the innards of the thin new machine.
The new iMac tapers to a 5mm thin edge along the sides, requiring the use of a special welding technique to achieve the design.
The 21.5" iMac will go on sale today in the U.S. both in retail stores and in the online Apple store with immediate availability. The 27-inch model will be available for pre-order but won't ship until December. Stock is expected to be tight throughout 2012.