iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Apple Releases iOS 4.2.1 Golden Master to Developers
MacRumors has just received word that Apple has seeded a new golden master of iOS 4.2, known as iOS 4.2.1, to developers. The new version carries a build number of 8C148, up from the previous 8C134.
According to those familiar with iOS 4.2.1, Apple has instructed developers not to resubmit their applications under the new build, suggesting that only minor fixes are included.