Owners of the Sprint flavor of the Galaxy Note 3, I have some good news: you're going to be using the latest version of Android for at least a month or two before the L release gets its public debut. Samsung's support site has posted the changelog for the Android 4.4.4 update, which means it should be heading out to end users soon. Not only is this the latest Android build for the Note 3, I think it might be the first build of 4.4.4 for any Samsung phone in the country.
Like most of the other Samsung flagship phones, the Sprint Note 3 has been running on 4.4.2 for the last several months. The update to 4.4.3 brings a lot of significant changes, and 4.4.4 is a few small but notable security fixes. In addition to the changes in AOSP, Samsung's support page says that the N900PVPUCNH7 update published today includes support for international Wi-Fi calling, Knox encryption version 2.0, and "Kids Mode," a super-simple and restricted interface first seen on the Galaxy S5.
Samsung's Android version updates tend to be pretty huge, so you'll definitely want to find a handy Wi-Fi network once you get the OTA update alert. If you've rooted or otherwise modified your phone, be aware that the update might fail to flash - check your favorite user forum for instructions on reversing your changes or flashing an older version. Like most carriers Sprint sends out its updates in batches, so don't be surprised if you don't see it coming in right away.