Traditionally, Nexus phones have been known for running "pure Google" Android software -- Android the way Google designed it, and the way manufacturers receive it before they make whatever modifications they see fit.
With the Nexus 5, it turns out only the first part of that concept is completely true. The Nexus 5 is the first phone to run Google's untouched vision of the Android 4.4 KitKat OS -- but KitKat as it appears on the Nexus 5 is not the same KitKat other devices will get.
This is unusual, I know. I was surprised when I first saw a passing mention of it in an interview-driven story at The Verge this week, so I reached out to Google to see what was actually going on.
Here's the deal, straight from the horse's mouth: Two parts of the Android 4.4 launcher seen on the Nexus 5 will, in fact, remain exclusive to the Nexus 5 -- at least for now. Those parts are the integration of Google Now into the home screen and the ability to activate Voice Search by saying "Okay, Google" while on the home screen.
The latter part isn't entirely surprising, as that functionality always seemed to be presented as more of a Nexus 5 feature than a core KitKat element (and it may require some level of hardware-specific integration in order to work efficiently). Keeping the new presentation of Google Now exclusive to one device is rather unexpected, though, since that's a strictly UI-oriented software element.
But for better or for worse, that part of KitKat will not appear on other Nexus devices -- or any other Android phones -- for the time being. The full statement provided to me by Google:
The Nexus program is about pushing the next generation of user experiences across software and hardware. As part of that, we're trying something new on Nexus 5 and we’ll see how users like it. Users have loved launchers from Google Play for some time now; in fact, some of the most popular launchers have been installed over 100 million times. For now the Google Now home screen integration and "Okay, Google" hot word is specific to the N5.
In other words, if you've got a Nexus 4, you'll get a slightly different version of KitKat than what's on the Nexus 5 -- one that looks the same for the most part but continues to provide Now as a standalone app instead of a panel within the home screen.
[UPDATE: Based on information presented in an official Google Android 4.4 Quick Start Guide, it appears that the new widget and home screen configuration utility, which ties into the Now home screen implementation, will also be limited to the Nexus 5 for the time being. I asked Google for clarification and the company has confirmed that is correct.]
It'll be interesting to see how this pans out in the long run.
• How to make your home screen look like KitKat -- without the Google Now panel
• Nexus 5 vs. Nexus 4: Worth the upgrade?
• Android 4.4, KitKat: The complete FAQ
• Android 4.4 upgrade list: Is your device getting KitKat?