Premium tier has three distinct advantages over the non-Premium version of the service: global connectivity, a larger number of virtual networks, and a larger number of routes (private and public peering).
Starting April 1, 2016, customers will be able to provision the Premium service by licensing a single plan instead of two (for example, non-Premium and Premium add-on). The Premium tier will be required for customers who use ExpressRoute to access Office 365 (Microsoft peering enabled). Customers with fewer than 500 seats who use ExpressRoute to access Office 365 can still purchase ExpressRoute Premium, based on the revised (lower) prices, effective April 1, 2016. On May 1, 2016, we’ll simplify the licensing experience for this offer, allowing customers to sign up for a single plan.
The revised pricing and new offers will be available through all existing channels. For more information on the offer for Office 365 customers who use ExpressRoute, please visit the Azure ExpressRoute for Office 365
page. For more information about pricing, please visit the ExpressRoute pricing