Caliburn.Micro always had the concept of Coroutines which allowed you to write asynchronous code in a synchronous way.
Starting from .NET 4.5 with the introduction of the async and await keywords, Microsoft introduced the concept of Coroutines in the language itself.
So if you want to use the same code in Caliburn.Micro with the async syntax, it becomes:
More information here: http://caraulean.com/blog/2013/07/15/using-caliburn-micro-with-async-await/