Github repo https://github.com/probcomp/Gen
Paper: https://dl.acm.org/citation.cfm?id=3314221.3314642 (is this article paywalled? I'm on my university's network so I don't have a paywall)
The syntax doesn't seem to be changed compared to Julia (so is it actually a new language or just a library? Not sure, haven't seen Julia code in a while.)
And the semantics are the same with some additions. This is a good thing as it allow interop with Julia code, low mental overhead and shows the power of Julia :)