WhatsApp is reportedly testing a new disappearing messages feature that will make messages vanish after being read. This builds on existing options that allow messages to disappear after 24 hours, seven days, or 90 days.
According to WABetaInfo, the new “After reading” timer will remove messages from the sender’s chat 15 minutes after sending, and from the recipient’s chat 15 minutes after reading. If the recipient does not open the message, it will disappear automatically after 24 hours.
Users will have the option to enable this feature for individual chats or as a default for all conversations. The update is still under development and expected in a future WhatsApp release.

