A quick search brings up this RFC to remove green threads [1] which is dated "2014-09-16". So, it's entirely likely that Rust (sure, pre-1.0) had green threads

A quick search brings up this RFC to remove green threads [1] which is dated "2014-09-16". So, it's entirely likely that Rust (sure, pre-1.0) had green threads around the time that the Java conversion happened. Although the only important thing is that WebAssembly is 2015 [2] so there's pretty much no reason to convert to Rust to target WebAssembly when neither of them were actually released. [1]: https://github.com/rust-lang/rfcs/blob/master/text/0230-remove-runtime.md https://github.com/rust-lang/rfcs/blob/master/text/0230-remo... [2]: https://en.wikipedia.org/wiki/WebAssembly#History https://en.wikipedia.org/wiki/WebAssembly#History