As of November 2nd 2018, we've made a change to our system to automatically track visitors beyond the active visitor caps assigned to each of your domains. We will continue tracking all visitor sessions during traffic increases, and all overage traffic will be captured in both your Real-Time and Historical Dashboards.
If you're expecting more than 2x your site's usual traffic levels, it's still a good idea to let your Customer Success Manager know in advance so we can ensure that proper server space is allocated for your site's traffic data.