How WhatsApp enables multi-device capability

This post details the technical architecture and security considerations for WhatsApp's new multi-device capability. It explains how WhatsApp moved from a smartphone-centric architecture to a standalone multi-device experience, addressing challenges in maintaining end-to-end encryption, synchronizing data across devices, and adapting voice/video protocols. Key technical contributions include the client-fanout approach for message delivery, new technologies for device identity management and verification, and methods for synchronizing message history and application states while preserving privacy.