The Google Assistant launched on Android with the Google Pixel phones, and since then it has been in an awkward position. The Google Assistant is one of the main interfaces for Google Search, Google's flagship product. Google is accustomed to serving billions of searches per day, but when Google made the Assistant exclusive to the Pixel phones, it limited the usage of the heavily-promoted interface to a tiny fraction of possible users.
Google is finally lifting the arbitrary limits on the Google Assistant and bringing it to all Android phones running version 6.0 and up—about 30 percent of active devices. Soon, an update to the Google Search app—which the Assistant is a part of—should arrive and enable the new voice interface on all devices that can handle it. Google is also opening up the Google Assistant to OEMs this week, with the just-announced LG G6 being the first to ship with the Assistant.
As for the full rollout details, Google says:
The Google Assistant will begin rolling out this week to English users in the U.S., followed by English in Australia, Canada, and the United Kingdom, as well as German speakers in Germany. We'll continue to add more languages over the coming year.
Google "rollouts" can take a few weeks, so don't expect it to pop up on your phone later tonight. Eventually a Google app update should enable it, though.
There isn't a huge difference in functionality right now between the Google Assistant and the old "Ok Google" voice interface. The Assistant has a new results interface that looks more like an IM app than the typical Google results page, and the Assistant is a lot more "human" now. Ask it to tell a joke, or what it's favorite color is, or play a crazy game show. The Assistant also adds a few smart home capabilities, provided you have the right hardware.
The wider release of the Assistant onto any modern Android phone is just the latest stage in Google's plan to get Assistant onto every Google product. Besides Android, the Assistant is also on Google Home, Android Wear 2.0, and Google Allo.It will soon arrive on Android TV and Android Auto. Google says its goal is to eventually "make the Assistant available anywhere you need it."