Google, at its I/O developer conference in Mountain View announced that the Assistant will be available on the iPhone. With the announcement of this Google will now directly take on Apple’s Siri and it will be really very interesting to see who will win the battle.
— Google (@Google) 17 May 2017
The performance of the Google Assistant on iPhone will not be exactly similar to that on the Android device because of the API restrictions on the iOS platform. And, you can’t remap the Home button on the iPhone from Siri to Google Assistant, but you can instead add a widget to access it.