Google Assistant is rolling out to millions of Android phones without the need for a carrier or manufacturer update, and that's a big deal.

From just two handsets to hundreds, Google has lifted the device restriction on its AI helper, Google Assistant.

Announced earlier this week, Google Assistant will replace Google Now and Now on Tap on any device running Android 6.0 and above that supports Google Play Services. That doesn't sound like a lot, but it is: nearly 32% of all Android phones are running Marshmallow or Nougat, which translates into nearly 500 million devices (if there are 1.5 billion active devices that can connect to the Play Store).

To access Google Assistant, one simply needs to hold down the home button on their device — the same method as accessing Google Now. The transition will take a few days to complete, since it involves receiving an updated version of Google Play Services, but once it rolls out it will be the single biggest update to Android in years that didn't have to be approved by a phone manufacturer or carrier. That's because Assistant fundamentally changes the way one uses an Android phone, shifting much of the interaction from text to voice.

Google Assistant, in addition to being on phones, is available on Android Wear 2.0 devices, Google Home, and, soon, Android TV through the NVIDIA Shield.

The rollout for phones will initially be limited to U.S. devices but will soon be available for English speakers in Australia, Canada and the United Kingdom, as well as German speakers in Germany. Google says more countries will come soon.

How to set up and customize Google Assistant on your phone