If you're on the WhatsApp Testflight program you'll see this update roll out soon, the rest of us will need to wait. That means that if someone gets hold of your unlocked phone they won't be able to access your WhatsApp chats without you authenticating yourself again. The program itself simply asks the phone if you're allowed access, iOS will either confirm or deny allowing WhatsApp to let you in. Anyone using iOS who wants to preview new features like this could apply to the Testflight for WhatsApp. Sometimes people do quit the Testflight beta program though, so it's worth keeping an eye on this page.

Source: Forbes February 03, 2019 16:07 UTC