On July 23, 2013, MulticoreWare released pre-alphasource code for x265. Development on x265 began in March 2013. The x265 project is funded by several companies that will direct the development requirements and receive commercial licenses to use x265 in their products without having to release their products under the GPL 2 license. The x265 project has licensed the rights to use the x264 source code for those features that can be used with HEVC. x265 source code is written in C++ and assembly.
The current release of x265 supports the Main profile of HEVC, which has a bit depth of 8-bits per sample YCbCr with 4:2:0 chroma subsampling, with limited support for the Main 10 profile. x265 supports many of the features of x264 including constant QP encoding, Average Bit Rate control, and lookahead. Some features such as weighted prediction and 10 bit encoding are supported but unoptimized. MulticoreWare has said that based on peak signal-to-noise ratio (PSNR) the decrease in bit rate when going from x264 to x265 will be between 25% and 35% and that coding efficiency for x265 will increase as improvements are made to the encoder. In a video comparison done in July 2013 by ExtremeTech with an encoding preset of veryslow it took 129 seconds to encode a video clip with x264 and 247 seconds to encode it with x265.