At 10×: the connection layer scales to hundreds of chat servers. The connection registry must handle millions of lookups per second — sharding Redis by user ID distributes this load. Message storage moves from a single database to a sharded append-only log per conversation.
At 100×: geographic distribution. Users in different regions connect to the nearest regional chat cluster. Cross-region message routing adds 100–200ms latency. Real-time chat across regions requires careful engineering of the connection registry and the cross-region message path.