According to Android Developer LlabTooFeR the upcoming version of Android Kit Kat 4.4.3 (build number KTU72B) is in testing phase and will fix the annoying camera bug currently present on the Nexus 5 which causes an increases in the CPU usage which then drastically affects the battery life of the device.
Other then the camera bug we don’t know much of what we can expect for the new version, we expect it to contain the usual bug fixes and performance enhancements to improve the user experience. According to the latest rumors the 4.4.3 update will be exclusive to Nexus devices as it will be a small update addressing the mayor camera bug and several other small bugs that are causing performance issues on Nexus devices.
Android 4.4.3 is under testing. Build number is KTU72B. Probably it will fix known camera bug.
— LlabTooFeR (@LlabTooFeR) March 24, 2014