The feature allows users to reply to any notification that pops up on the device right from the Notification Centre without opening the app. They can do so by just dragging down a notification to type a reply. For example, if someone receives a text notification, just pull it down and reply without opening the app. The WhatsApp version 2.12.10 is now available to download via App Store and measures about 50MB in size.
An earlier report had tipped the feature was incoming, as iOS 9.1 beta users were seeing a Quick Reply option with the latest build of WhatsApp.
The update also brings feature that allows users to reply to incoming WhatsApp calls with a message right from the call notification.
Last month, WhatsApp for iOS added support for 3D Touch on the new iPhone 6s and iPhone 6s Plus. WhatsApp for iOS update bumped the version to 2.12.9 and primarily introduced 3D Touch support alongside other minor updates.
With the addition of 3D Touch input to the WhatsApp for iOS, iPhone 6s and iPhone 6s Plus users could use 'Peek and Pop' gestures based on the pressure applied on the screen.