WhatsApp is developing a new feature that summarises your unread chats to make it easier for you to catch up on the messages you missed. The feature has been under development for some time, and is currently rolling out to beta users on Android.
According to WABetaInfo, the feature that uses Meta AI to generate summaries can be enabled by turning on the Private Processing toggle. The feature is showing up in WhatsApp beta for Android version 2.25.15.18, which is now available on the Google Play Store.

When Private Processing is turned on, users should see a description of what the feature can do. In future releases, it should also help users write better with better wording and style suggestions, and these features are marked as "coming soon". Meta says that nor it or WhatsApp can read users messages as they're processed privately, on-device.
Once the feature is active, users will see a Summarise with Meta AI option for long incoming messages and it will show up at the top. Tapping on this option will give prompt Meta AI to share a brief summary of the messages.
It's worth noting that the feature is entirely optional. It's also disabled in conversations with Advanced Chat Privacy is enabled. Messages summaries should come in handy for users whose primary mode of communication is WhatsApp, and end their day with lots of unread messages. It's similar to Apple's Notification Summaries, but one that works inside WhatsApp and doesn't need a high-end device to power it.
The Messages summaries feature is currently rolling out to the beta users of WhatsApp on Android, meaning users on the stable version will have to wait a few more weeks. There's no mention of the feature's available on the app's iOS version yet.