All the signs are showing that the folks at Google are on the way of releasing the Android 4.4.3 update for the supported devices. Since Sprint announced their Nexus 5 variant will be updated to the latest firmware, Android 4.4.3 has been spotted several times.
If you want further proof that the Android 4.4.3 update is on its way, hear that the new firmware has been spotted running on a Sony Xperia Z Ultra Google Play Edition that recently received Bluetooth SIG certification.The device in case was running a new software version labelled "KTU72.S1.3013." As you may know, KTU72 is the an Android 4.4.3-specific build. Unfortunately, except for the fact that the new update will arrive on most Nexus experience handsets, the Bluetooth SIG listing doesn't offer more information about the new firmware.
The Android 4.4.3 update was also spotted in Play Store, after Google updated the changelog of the Edu Device Setup app. The what's new section of the Edu Device Setup notes that after the new update it has "support for Android 4.4.3 and non-Nexus tablets," which might indicate that the new update will be pushed to users soon.
As I was mentioning above, Sprint was the first carrier to announce that the Android 4.4.3 update will be rolled out for their Nexus 5 variant, but since the announcement was made we didn't see a materialization. Anyway, the first time we've heard about Android 4.4.3 was in March, when it was reported that the new update will arrive to fix the Nexus 5 camera bug.
For the time being, Google didn't make an official statement on the arrival of Android 4.4.3, not to mention about an ETA. Even though it was initially believed that the update will only be released for the Nexus 5 owners, the latest reports are suggesting that the update will be released for all supported devices, including Nexus 4, Nexus 7, Nexus 7 2013, Nexus 10, along with Google Play Edition devices.