WhatsApp users will now have the option to turn on disappearing messages by default for all new chats. When enabled, all new one-on-one chats you or another person start will be set to disappear at your chosen duration, and we've added a new option when creating a group chat that lets you turn it on for groups you create. This new feature is optional and does not change or delete any of your existing chats.
WhatsApp is also adding two new durations for disappearing messages: 24 hours and 90 days, as well as the existing option of 7 days.
For people who choose to switch on default disappearing messages, we will display a message in your chats that tells people this is the default you’ve chosen. This makes clear it's nothing personal - it's a choice you've made about how you want to communicate with everyone on WhatsApp moving forward. Though of course, if you need a particular conversation to remain permanent, it’s easy to switch a chat back.
To get started, go to your Privacy settings and select ‘Default Message Timer’.
News Source: WhatsApp Blog