Still no support for threads running in parallel? I guess things didn't go well: https://news.ycombinator.com/item?id=9582980
There are a number of much anticipated features that haven't made it into this release. In particular, the multicore GC, which at one point had been expected to land in 4.03, has been pushed back, likely to 4.04.
~~ Well, I know, it's hard. ..
Jane Street certainly contributes a huge amount to the ecosystem, both in terms of code and other support, but they're not the only people pouring effort into it.