public static async Task ExecuteAsync() { var client = new HttpClient(); //client.DefaultRequestVersion = new Version(2, 0); // boost a bit with http2 var service = new ContactsService(client); var contact = await service.GetContactAsync(4123); Console.WriteLine($"{contact.EmailAdress}"); var response = await service.DownloadAsync("234"); await service.UpdateContactAsync(contact); var start = DateTime.Now; var tasks = new List <Task>(); for (int i = 0; i < 500; i++) { var task = Task.Run(async() => { Console.Write(">"); var list = await service.GetAllAsync(); Console.Write("<"); }); tasks.Add(task); } ; Task.WaitAll(tasks.ToArray()); Console.WriteLine($"{DateTime.Now - start}"); }