WhatsApp is currently working on adding support for up to 1,024 participants for each group. If that doesn’t sound hellish to you, then you’ll be happy to know that you should expect this feature to roll out to everyone soon. Currently, it’s in beta testing, with some beta testers seeing it, while most aren’t. Previously, WhatsApp added support for 512-member groups back in June
If you have the latest beta for either Android or iOS you should eventually get this feature. If you’re not part of WhatsApp’s beta testing, then rest assured that this will eventually make it to all users