While no US carrier-branded variants of the Galaxy S4 have received an official update to Android 4.4/KitKat yet, Samsung has dropped the KitKat kernel source for the Sprint's model. While that by itself is really only of interest to developers, its implications will matter to a much larger audience. Generally, Samsung does not release kernel source for builds that aren't official. Historically, once source code is made available, official OTA updates follow in reasonably short order.
The Galaxy S4 is upon us. AT&T and US Cellular launched their respective pre-order pages just yesterday, and now Sprint and T-Mobile have announced official release date and pricing info.
The Now network will begin offering The Next Big Thing on April 27th for the expected price of $250 with a two-year agreement. However, if you're willing to ditch your current provider and port your number to Sprint, you'll get another hundred-spot off, bringing the price down to $150.