IBM i 7.3 was made Generally Available on 12 Apr 2016.
IBM now deliver functional improvements between major releases via the Technology Refresh mechanism. A TR is a Group PTF which packages all of the PTFs needed to deliver the new functionality. Associated with that PTF group is a marker PTF. If you do a DSPPTF and see a particular marker, you know what TR level you're on. ²Detailed description of Technology Refresh content can be found in developerWorks, under IBM i Technology Updates Hardware and Firmware.
|TR3||27 Oct 2017||JSON publishing, Install IBM i from USB|