Currently, we recommend you use channel multiplexing for up to 10 (ten) channels. If your app requires a single client to subscribe to more than 10 channels, we recommend using channel groups

You can add up to 2000 channels to a channel group. When a client subscribes to that channel group, they are subscribed to all channels in that channel group. And each client can subscribe to 10 channel groups for a total of 20,000 channels.