SpecFlow supports using async methods as step definitions since version 2.2. Features requiring asynchronous execution can now be written in a more C#-ish style.

[Given("(.*)")]
public async Task GivenStep()
{
    await GetSomeTask();
}

Instead of writing your own state machine for awaiting tasks, SpecFlow has implemented this feature for you.

This example shows how to implement a step definition which calls the HttpClient.GetAsync method.