Google just took to its G Suite blog to break the news that it will officially begin to remove the Contacts button in all versions of Gmail, both legacy and new, app and web, effective immediately. While this was announced on the G Suite blog, the change seems to affect both enterprise and consumer editions of Gmail. In some cases, it seems that the option to pull up the Contacts menu within the Gmail interface is still present, but activating said option does nothing. It's worth noting that the shortcut was already gone for everybody on the new Gmail interface, which became the default a few months ago except for those who specifically opted out of it and went back to the old version.
To be clear, you'll really only know this change occurred if you specifically chose to go back to classic Gmail. The Contacts shortcut was gone in the mobile version of Gmail for quite some time, and it was never included in the Gmail reboot that was pushed out to desktop users a few months back. Users will now have to hit the apps icon near the top right of the Gmail window and go to the Contacts Preview through there. For G Suite administrators that may have disabled the feature some time ago and forgotten about it, Google has automatically reinstated access for all G Suite installations.
This change, as with many changes made in the past few months, is merely part of a larger effort that Google's been making to push Material Design updates to all of its products. Gmail has long been a mainstay of the Google arsenal, and effectively got its turn long ago. This is just the final nail in the old contact manager interface's coffin, so to speak. In time, users can expect similar changes across most of Google's product range, if not in everything, while the company works to unify its design language across all of its products. Those few administrators who still want access to the in-window Contacts interface for whatever reason can contact Google via the source link to ask for it.