According to Google, admins now have the capability to move their users over to using Google Chat instead of the classic Hangouts app. Google also notes that hangouts.google.com will still be available to visit. So this migration won't lock you out of using the website.
What it will do is replace all the classic Hangouts apps that organizations use. As well as replace Hangouts inside of Gmail with Google Chat as the default communication tool.
The G Suite Google Chat migration is essentially opt-in
Admins wanting to migrate all of the employees at their organization from Hangouts to Google Chat are not required to do so.
This is essentially an opt-in, and admins have the choice to move everyone over or not. The way this works is that there is a new setting in the admin console that is called "chat preferred." If this option is selected, then this initiates the migration over to Google Chat as the default tool.
But while this isn't a mandatory thing that Google is forcing G Suite customers to do, it is strongly encouraging them to make the change. Google highlights numerous benefits that follow after migrating over to Google Chat.
Including things like the ability to seamlessly communicate without having to switch tabs. There are other features that Hangouts also doesn't provide that Google Chat does. Such as bot integrations, full-screen rooms, emoji reactions and more.
Across the board there are a handful of features that Google feels make the migration worth it. And it definitely wants G Suite customers to know about all these benefits.
Chat Preferred is disabled by default
As noted earlier Google set this up as an opt-in process. As such, the toggle setting to use Chat Preferred is disabled by default.
Because it's off by default teams would still be using Hangouts until the switch is made by admins. That being said, admins won't be able to toggle this setting on right away. At least not all of them.
Google says the rollout for the new setting could take up to 15 days for feature visibility. It also just started rolling out this change as of June 2. So some admins won't see the option to toggle this on for another couple of weeks.
Google is also rolling out an ability to migrate employees on an organizational unit level. Which basically means group by group. Though that won't be rolled out until sometime in the coming weeks as well. For now, any migrations happen all at once.