Got it from here : https://infosec.exchange/@mattburgess/111885761552024420

NEW: WhatsApp will soon make it possible to chat with people who use other messaging apps. It’s revealed some more details on how that will work.

— Apps will need to sign an agreement with Meta, then connect to its servers.

— Meta wants people to use the Signal Protocol, but also says other encryption protocols can be used if they can meet WhatsApp’s standards

— WhatsApp has been testing with Matrix in recent months, although nothing is agreed yet. Swiss app Threema says it won’t become interoperable