A future version of WhatsApp will allow more than four users to participate in group audio and video calls. There is no word about what the revised upper limit will be just yet. Since the feature is still in development, it will be a while before it is available to everyone.
https://www.notebookcheck.net/WhatsApp-will-soon-allow-more-users-in-group-audio-and-video-calls.461872.0.html