Well, that was unexpected! After dozens of leaks leading up to the eventual release of Android 4.4.3, Android 4.4.4 has suddenly arrived without so much as a moment's notice. The update itself has not yet begun rolling out to actual end user devices, but just like what we saw with 4.4.3 KTU84M, the factory images have been posted for the majority of the current generation Nexus fleet.

Today’s Android 4.4.4 builds come in at KTU84P for the Nexus 5, Nexus 4, Nexus 7, Nexus 7 (2013), and Nexus 10. Unfortunately, just as was the case with 4.4.3 KTU84M, nothing is available for the Nexus 7 (2013) LTE-enabled variant at this time. According to Sprint's update support documentation released earlier today, this update only brings an unspecified "security fix." No details are known at present if this build fixes the Linux kernel CVE-2014-3153 vulnerability that was exploited by geohot in towelroot, but it wouldn't be much of a surprise if that were to be the case. Obviously, the earlier merge to kill Dalvik and implement ART as default runtime compiler has not yet made it to shipping builds.

You can get your fix by updating your device directly via the Nexus Factory Images page. And if building custom ROMs is your thing, grab the KitKat MR2.1 Source Code and then head over to the Nexus Driver Binaries page to get started.

Update: As pointed out by XDA Senior Member phaseL, this indeed does not implement a fix to the Linux kernel CVE-2014-3153 vulnerability exploited in geohot's towelroot, as the kernel build date (Mar 13) was dated well before a patch was made available (June 3).

[Many thanks to XDA Forum Moderator laufersteppenwolf, Recognized Developer iurnait, and Senior Member bilal_liberty for the heads up!]