A version of the IMA SDK will be supported for 12 months after its successor is released. After that time it will be deprecated.
The differences between a supported and deprecated version:
Developers are encouraged to include the latest IMA SDK each time they release their app to avoid the deprecation dates. The latest SDK's deprecation date doesn't get set until a newer SDK is released, so even apps with a 1-year release cycle can always stay on a supported SDK.