Google announced in September that it would be shuttering the app toward the end of March 2019, but didn't give a set date for when that would happen.
However, as noted on Reddit, users of the app yesterday began being notified that the app would be "going away in 15 days," which points to April 2 as the end date.
Inbox by Gmail was an experimental email app, offering users features like snoozing emails to check later, Smart Reply, high-priority notifications, and more.
Google says that in the four years of the app's life it "learned a lot about how to make email better," adding some of the most popular Inbox features directly into its main Gmail client, to which the company is directing existing Inbox users.
To help users transition from Inbox to Gmail, Google has set up a guide on its support website. Google says the new Gmail app, launched in April 2018, will be a good home for former Inbox users as it incorporates many of the same features as Inbox, in addition to new ones.