dotnet-core/release-notes/3.0/api-diff/3.0.0_System.Net.Http.md

System.Net.Http

 namespace System.Net.Http {
     public class HttpClient : HttpMessageInvoker {
+        public static IWebProxy DefaultProxy { get; set; }
+        public Version DefaultRequestVersion { get; set; }
     }
     public class HttpResponseMessage : IDisposable {
+        public HttpResponseHeaders TrailingHeaders { get; }
     }
     public class MultipartContent : HttpContent, IEnumerable, IEnumerable<HttpContent> {
+        protected override Task<Stream> CreateContentReadStreamAsync();
     }
     public sealed class ReadOnlyMemoryContent : HttpContent {
+        protected override Task<Stream> CreateContentReadStreamAsync();
     }
 }