Looks like they have compiler support for only C# (csc), and F# (fsc) right now.
https://github.com/dotnet/cli/tree/master/src/Microsoft.DotN...
https://github.com/dotnet/cli/tree/master/src/Microsoft.DotN...
https://github.com/dotnet/cli/tree/master/src/Microsoft.DotN...
https://github.com/dotnet/cli/tree/master/src/Microsoft.DotN...
c# is used to bootstrap all tools, so it's the first supported language and the default. Nightly, dev build have f# support, but it's a beta ( merged last week, but it's ok ).
f# dotnet cli (the wrapper for f# compiler) is a beta, but moving fast, not much todo. For example the f# support in dotnet new is in a pull request.
The F# compiler built for coreclr ( bundled with dotnet cli, so ready to go ) is working pretty much, some stuff missing ( portable pdb for example ),
f# coreclr is open source https://github.com/Microsoft/visualfsharp