Screenshots source: Gmail
Gmail's interface update has been rolling out for a while (at least since February). But Google is starting to push it out to more users, turning the experience into an opt-out instead of an opt-in. I've already spotted it in one of the Gmail accounts I have. This new look brings the Material You styling to Gmail while moving Chat, Spaces, and Meet into one area.
Since I don't use these varied messaging services on the Gmail account where the redesign has appeared, I no longer see the Chat box at the bottom of the Inbox and Labels panel. You can choose which apps will appear by heading into the Quick Settings menu.