This was a regularly scheduled release with improvements in performance, major improvements in memory usage, and improved psy-rd behavior.
There were a few of new options introduced:
—cu-stats, x265_param.bLogCuStats — enabling logging of CU stats (for R&D purposes only)
—hrd, x265.bEmitHRDSEI — enable HRD SEI signaling (use this option to add Hypothetical Reference Decoder information into the HEVC bitstream, in order to comply with HRD specifications)
—ipratio/—pbratio were exposed to the CLI
—lambda-file — allows experimentation with lambda tables (for R&D purposes only — this should not be needed for normal production encoding purposes)
Plus a number of options added for multi-pass encoding (incomplete).