iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Apple Seeds First OS X 10.9.2 Build to Developers [Update: Includes FaceTime Audio]
Apple cites no known issues with the build and asks that developers focus their testing on the following areas: Mail, Messages, VPN, Graphics Drivers, and VoiceOver.
There is no word yet on specific fixes and changes included in the update, and a public release target remains unknown.
Update: OS X 10.9.2 adds FaceTime Audio to the Mac for the first time. FaceTime Audio was originally introduced to the iPhone in iOS 7.