Also keep in mind our clients aren't just idle WS processes. They start a channel process for each topic they join ("rooms:lobby") in this case. So 1 WebSocket

Also keep in mind our clients aren't just idle WS processes. They start a channel process for each topic they join ("rooms:lobby") in this case. So 1 WebSocket connection will spawn two processes. One for the transport (WS handler), and one for the channel. The channel also holds its own state, which is mostly empty, but carries metadata, so it's hard to compare to your 500k raw connections.