We just saw HTC post its KitKat open source files for the Google Play Edition One, and now here's Samsung doing the same thing for the GPe Galaxy S4. Although, its open source website is a lot less attractive. What's with that, Samsung? At any rate, you can grab the kernel source right now at the link below.
The download is 399MB and contains all the open source bits of the updated ROM. It's not a full system image or anything like that. It's mainly developers who will be interested in what this ZIP file contains. We haven't heard any sort of announcement from Samsung that its GPe ROM has been submitted to Google, but Samsung isn't as up-front with such things.
Still, getting the kernel source means the OTA must be almost ready to go out. It's probably too soon to start mashing the update button, but you can still do it if it makes you feel better.