The beta version of WhatsApp explores the possibility of having only one user account for up to four devices.
WEBetaInfo has reported that WhatsApp has begun testing multiple device log ins using only a single account. The app can send verification codes in order for log ins to additional devices to be successful. However, the security details for the update hasn’t been fully fleshed out yet.
Currently in the iOS version WhatsApp users will need to have a number to access the app on an iPhone, and this can’t be used on another phone. Losing your number equals a lost WhatsApp account. With the new changes iOS users can link their WhatsApp accounts to devices, similar to the WhatsApp for Web feature.
The functionality is hidden in beta versions and therefore unusable. As such, it can appear in future iterations or not at all- WhatsApp could just be testing it out to see if it can be done.