VMware NSX has four licensing editions: standard, advanced, enterprise, and remote office/branch offices (ROBO). Each licensing tier provides distinctive functionality, available per CPU socket on a perpetual basis at the vSphere cluster level.
The standard and advanced editions are also available as per 100 users in a pack basis to align with virtual desktop deployments (vSphere for desktop). The enterprise edition is also available on per-VM term basis. You can upgrade from standard to advanced/enterprise and from advanced to enterprise.