https://www.techradar.com/news/whatsapp-group-calls-are-now-live-for-android-and-ios

Up to four people can now chat at once using WhatsApp for Android and iOS. The new group call feature is rolling out to both platforms at the same time, and lets app users set up multi-way video or voice calls.

To use it, start a call with just one person, then tap the 'Add participants' button in the top-right to invite more friends. The new participant will receive a notification, and can choose whether to accept or decline.