By design both Test Studio Ultimate and the underlying Telerik testing framework run synchronously. This said, you can still write and run "async" methods but you will have to wait for the the task(s) to complete. For example:
"New Coded Step"
async Task<System.Net.Http.HttpResponseMessage> GetStatusForUri(
var client =
Here we create a task that will synchronously wait blocking execution until the async one is completed.
Hope this helps. Please, let me know if you have further questions.