AFAIK green threads were removed from the core language but are available as crate green (also known as greenlib). You can use that for building servers.
They're gonna get yanked out of the core distribution too and won't be integrated in the stdlib IO anymore, so it's fair to say that Rust is switching to 1:1 threading.
The decision was made around https://github.com/rust-lang/rfcs/pull/230 but I'm not sure whether there's any important prior discussion not linked from there, the topic has been kicked around for a bit.