According to Android Geeks
, a leaked chart from Samsung indicates that the Galaxy S5 will start receiving 4.4.3 this month, and the S4 in July. Carrier branded versions will probably lag behind by a couple of months or more, depending on the carrier.
KitKat 4.4.3 for the Google Nexus and Motorola phones is little more than a bug fix, so don't get too excited. But if you've noticed any minor bugs with 4.4.2, this may improve your experience.
Android Geeks says they can't verify the authenticity of the chart above, so put this in the rumor category. But it does fit with earlier leaks that Samsung was actively working on 4.4.3 on these devices.