The Nexus 5 comes with a fancy new launcher, internally called "Google Home," that integrates the Google Search app and the home screen. All that means on the surface is that users have slightly easier access to search and Google Now, but under the hood there are huge changes—the entire home screen is being drawn by Google Search.
Despite being a headline feature of KitKat and being integrated into Google Search (which ships on every Android device), Google has stated that the new launcher is exclusive to the Nexus 5. We find that a little hard to believe—why would Google integrate something into its most popular app if it didn't intend to ship it out to as many people as possible? The "Google Home" version of Search that came with the Nexus 5 was version 3.0, while the version of search that most devices had at the time was version 2.8.
Late yesterday, a new version of Google Search hit the Play Store for everyone running Android 4.1 and higher—Google Search version 3.1. All the Google Home code was completely intact, meaning that Google just shipped its new launcher out to every modern Android phone. In order for Google Home to work, it requires a tiny enabler app that comes with the Nexus 5. The enabler app isn't being shipped out to these other devices, so while 99 percent of the code is now on everyone's device (or it will be when the rollout finishes), it's disabled.