Consider FileStreamResponse Handler

[DalSoft]

public class FileStreamHandler : DelegatingHandler
    {
        public static string FileStreamHandlerKey = nameof(FileStreamHandlerKey);
        
        
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            return await base.SendAsync(request, cancellationToken)
                .ContinueWith(task =>
                {
                    var response = task.Result;

                    if (response.Content.Headers.Contains("Content-Disposition"))
                    {
                        request.Properties[FileStreamHandlerKey] = response.Content.ReadAsStreamAsync().Result;
                        response.Content = null;
                    }

                    return response;

                }, cancellationToken).ConfigureAwait(false); // Next in the pipeline
        }
    }




        [Test]
        public async Task Stream_UsingHttpResponseMessage_CorrectlyStreams()
        {
            dynamic restClient = new RestClient("https://github.com", new Config(new FileStreamHandler()));

            HttpResponseMessage response = await restClient
                .Headers(new { Accept ="application/octet-stream" })
                .Resource("tugberkugurlu/ASPNETWebAPISamples/archive/master.zip").Get();

            var savePath = Path.GetTempPath() + "master.zip";
            var stream = response.RequestMessage.Properties[FileStreamHandler.FileStreamHandlerKey] as Stream;
            
            if (stream == null)
                return;

            using (var fileStream = File.Create(savePath))
            {
                stream.CopyTo(fileStream);
            }
        }