There was a major code dump in September that added support for ProRes decoding, and another in October that added encoding support. There has been a lot of incremental work to improve them since that time.
However, I don't believe that any of the official release builds have it built in yet since it is still experimental. You would need to build from git sources if you wanted to test it out.
It certainly does now - both encodes and decodes, I use it all the time.
eg ffmpeg -i input.mov -vcodec prores -profile hq -acodec pcm_16sle output.mov will turn input.mov into a prores 422 (HQ) file (the -acodec option is given just because that's how fcp likes it).