Cycles hair rendering - nowhere to be found

Hi !
I wanted to try out the new cycles hair rendering feature, so I downloaded the latest build I could find (r54336) but there’s no way I can find the option, in the particle systems settings, to enable it. I switched from GPU to CPU and did a few tests with different builds from different locations etc. So… Am I missing something ?

It’s Cycles, CPU and Experimental Feature set instead of Supported.

Thank you. (Just realised I’m in the wrong category, sorry for that.)