API Implementation Statuses
A status of "Planned" for an API feature means that this is slated for implementation and will definitely be implemented at some point in time. When a feature/resource is marked as planned, it means that all information in the wiki regarding it is used for planning purposes, and is subject to change (moreso than other features which have at least a partial implementation already).
See the API Feature Planning page for information on how to share feedback with the developers regarding planned and future API features.
A status of "Under Development" for an API feature means...well, that's obvious.
A status of "Implemented" for an API feature means that it is implemented and "more or less" ready for use. The URIs are not likely to change at this point, however responses may be added to - when consuming responses generated by this API, you should always be able to handle extra dictionary items.