x265 version 1.9 has now been released. This release supports many new features as well as additional assembly optimizations for Main12, intra prediction and SAO. Recently added features lookahead-slices, limit-refs and limit-modes have been enabled by default in the supported presets.

Full documentation is available at http://x265.readthedocs.org/en/stable/

========================= New Features =========================
Quant offsets: This feature allows block level quantization offsets to be specified for every frame. An API-only feature.
--intra-refresh: Keyframes can be replaced by a moving column of intra blocks in non-keyframes.
--limit-modes: Intelligently restricts mode analysis.
--max-luma and --min-luma for luma clipping, optional for HDR use-cases
Emergency denoising is now enabled by default in very low bitrate, VBV encodes

========================== API Changes =========================
x265_frame_stats returns many additional fields: maxCLL, maxFALL, residual energy, scenecut and latency logging
--qpfile now supports frametype ‘K»
x265 now allows CRF ratecontrol in pass N (N greater than or equal to 2)
Chroma subsampling format YUV 4:0:0 is now fully supported and tested

===================== Presets and Performance =====================
Recently added features lookahead-slices, limit-modes, limit-refs have been enabled by default for applicable presets.
The default psy-rd strength has been increased to 2.0
Multi-socket machines now use a single pool of threads that can work cross-socket.