Apple has recently announced to launch official SDK for Apple Watch named Watchkit on November 12th, 2014.
WatchKit will give developers the tools needed to build app for the Apple Watch. This was announced by Tim Cook a few days back in the Apple event.
Apple has named this SDK Watchkit in resemblance with HealthKit and HomeKit.
The release of Apple Watch is scheduled to early days of 2015 whereas SDK will be available to the developer in November, possibly till 12th of November.