Some parts of Graal (like ahead of time) were added in Java9 on Linux 64bit, rest of the Graal was added to Java10, but also only for Linux 64 bit. Graal is pretty much workable but there are some edge cases that crash your code or the JVM, eg. Ruby generally works, but Ruby on Rails doesn't.
*Still hoping Oracle will be so good to allow TruffleRuby download without all the signing up and agreement.