PubNub can support millions of concurrent connections. Consider that PubNub has thousands of customers and many of those customers have millions of customers that are connecting to PubNub and sending/receiving messages constantly to the order of billions of transactions per day.

If you know that your application will have more than 1000 concurrent connections (devices/user), you should contact us to discuss a Pro plan to take advantage of volume discounts and included best practice architecture review by one of our experts to optimize your application. 

Please contact PubNub Support for more details.