It may be officially dead, but if you still want to use Inbox by Gmail for at least a few more checks on your messages, we have some good news: you can delete the app and download an older, working version from APK Mirror!
Version 1.78, released in October, was the last for the email client. Users who tap into it from today onwards will see an animated splash screen and a message urging them onto the main Gmail app:
Redditors in the r/Android community who refused to accept the demise of Inbox decided to pull up older versions of the app just to see if they worked. We checked it out ourselves and were able to affirm that we could manage reminders and receive messages with the v1.77 APK from September. We also were able to make Inbox work with v1.72 from May.
We suspect that Google will catch up to this discovery and cork up the floodgates. Either that, or it lets everyone ride the bull into the server shutdown. Nothing in life is for certain.