Free or two commercial editions, pricing for Standard Edition is: $763 / socket, Premium: $1525/ socket - both including 1 year of software maintenance.
The Express Edition provides a reduced set of features and is not eligible for Citrix Support and Maintenance. Express Edition does not require a license. Hosts that are running the Express Edition of Citrix Hypervisor are labeled as “Unlicensed” in XenCenter.
Express Edition was called Free Edition in previous releases of Citrix Hypervisor. The name of the edition has changed to align with other Citrix products, but the features and capabilities provided by the edition have not changed.
For commercial editions (Standard or Enterprise) XenServer is licensed on a per-CPU socket basis. For a pool to be considered licensed, all XenServer hosts in the pool must be licensed. XenServer only counts populated CPU sockets.
All customers who have purchased any edition of XenApp or XenDesktop have an entitlement to use all Citrix Hypervisor features
From version 6.2.0 onwards, XenServer (other than via the XenDesktop licenses) is licensed on a per-socket basis. Allocation of licenses is managed centrally and enforced by a standalone Citrix License Server, physical or virtual, in the environment. After applying a per-socket license, XenServer will display as Citrix XenServer Per-Socket Edition.