The new version of Inbox Android have undo action feature. How this new feature will help you: You can now undo an action taken inside a notification. It was the major change we found in this update.
Else, we found the performance improvement and the bug fixes in this update.
Above changes we found by exploring the APK update. We installed it on Nexus 6p.
Go to the below link to download the APK file of this update.
Inbox by Gmail v1.50 APK to Download