Android 4.4.3 tipped by one of Google's apps

App that helps schools set up tablets mentions Android 4.4.3 in recent changelog

Android 4.4.3 still hasn't been officially announced or anything, but it's still officially pinging our servers, and not in a way that suggests it's just kids playing with their build.prop file. And on April 16 the Google Edu Device Setup app — an official app straight from Google that helps set up tablets purchased through Google Apps for Education — was updated for Android 4.4.3 support.

source: androidcentral