diff --git a/Directory.Build.props b/Directory.Build.props
index 37ebc0356f..fbb0c081f2 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -16,6 +16,8 @@
     <SignAssembly>true</SignAssembly>
     <PublicSign Condition="'$(OS)' != 'Windows_NT'">true</PublicSign>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <!-- https://github.com/aspnet/BuildTools/issues/592 -->
+    <EnableApiCheck>false</EnableApiCheck>
   </PropertyGroup>
 
 </Project>
diff --git a/build/dependencies.props b/build/dependencies.props
index 6268a57dd7..544fc9100f 100644
--- a/build/dependencies.props
+++ b/build/dependencies.props
@@ -40,6 +40,7 @@
     <SerilogExtensionsLoggingPackageVersion>1.4.0</SerilogExtensionsLoggingPackageVersion>
     <SerilogSinksFilePackageVersion>3.2.0</SerilogSinksFilePackageVersion>
     <SystemDiagnosticsDiagnosticSourcePackageVersion>4.5.0-preview2-26224-02</SystemDiagnosticsDiagnosticSourcePackageVersion>
+    <SystemIOPipelinesPackageVersion>4.5.0-preview2-26224-02</SystemIOPipelinesPackageVersion>
     <SystemReflectionMetadataPackageVersion>1.6.0-preview2-26126-03</SystemReflectionMetadataPackageVersion>
     <SystemServiceProcessServiceControllerPackageVersion>4.5.0-preview2-26224-02</SystemServiceProcessServiceControllerPackageVersion>
     <XunitPackageVersion>2.3.1</XunitPackageVersion>
diff --git a/src/Microsoft.AspNetCore.TestHost/HttpContextBuilder.cs b/src/Microsoft.AspNetCore.TestHost/HttpContextBuilder.cs
index 4617be5308..6886b1aac4 100644
--- a/src/Microsoft.AspNetCore.TestHost/HttpContextBuilder.cs
+++ b/src/Microsoft.AspNetCore.TestHost/HttpContextBuilder.cs
@@ -90,14 +90,14 @@ namespace Microsoft.AspNetCore.TestHost
             {
                 _requestAbortedSource.Cancel();
             }
-            _responseStream.Complete();
+            _responseStream.CompleteWrites();
         }
 
         internal async Task CompleteResponseAsync()
         {
             _pipelineFinished = true;
             await ReturnResponseMessageAsync();
-            _responseStream.Complete();
+            _responseStream.CompleteWrites();
             await _responseFeature.FireOnResponseCompletedAsync();
         }
 
diff --git a/src/Microsoft.AspNetCore.TestHost/Microsoft.AspNetCore.TestHost.csproj b/src/Microsoft.AspNetCore.TestHost/Microsoft.AspNetCore.TestHost.csproj
index a2fdc53e9c..92a0795d05 100644
--- a/src/Microsoft.AspNetCore.TestHost/Microsoft.AspNetCore.TestHost.csproj
+++ b/src/Microsoft.AspNetCore.TestHost/Microsoft.AspNetCore.TestHost.csproj
@@ -18,4 +18,8 @@
     <ProjectReference Include="..\Microsoft.AspNetCore.Hosting\Microsoft.AspNetCore.Hosting.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="System.IO.Pipelines" Version="$(SystemIOPipelinesPackageVersion)" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/Microsoft.AspNetCore.TestHost/ResponseStream.cs b/src/Microsoft.AspNetCore.TestHost/ResponseStream.cs
index 9471e5e872..0cd3459a80 100644
--- a/src/Microsoft.AspNetCore.TestHost/ResponseStream.cs
+++ b/src/Microsoft.AspNetCore.TestHost/ResponseStream.cs
@@ -2,9 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Concurrent;
+using System.Buffers;
+using System.Diagnostics;
 using System.Diagnostics.Contracts;
 using System.IO;
+using System.IO.Pipelines;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -17,38 +19,20 @@ namespace Microsoft.AspNetCore.TestHost
         private bool _complete;
         private bool _aborted;
         private Exception _abortException;
-        private ConcurrentQueue<byte[]> _bufferedData;
-        private ArraySegment<byte> _topBuffer;
-        private SemaphoreSlim _readLock;
         private SemaphoreSlim _writeLock;
-        private TaskCompletionSource<object> _readWaitingForData;
-        private object _signalReadLock;
 
         private Func<Task> _onFirstWriteAsync;
         private bool _firstWrite;
         private Action _abortRequest;
 
+        private Pipe _pipe = new Pipe();
+
         internal ResponseStream(Func<Task> onFirstWriteAsync, Action abortRequest)
         {
-            if (onFirstWriteAsync == null)
-            {
-                throw new ArgumentNullException(nameof(onFirstWriteAsync));
-            }
-
-            if (abortRequest == null)
-            {
-                throw new ArgumentNullException(nameof(abortRequest));
-            }
-
-            _onFirstWriteAsync = onFirstWriteAsync;
+            _onFirstWriteAsync = onFirstWriteAsync ?? throw new ArgumentNullException(nameof(onFirstWriteAsync));
+            _abortRequest = abortRequest ?? throw new ArgumentNullException(nameof(abortRequest));
             _firstWrite = true;
-            _abortRequest = abortRequest;
-
-            _readLock = new SemaphoreSlim(1, 1);
             _writeLock = new SemaphoreSlim(1, 1);
-            _bufferedData = new ConcurrentQueue<byte[]>();
-            _readWaitingForData = new TaskCompletionSource<object>();
-            _signalReadLock = new object();
         }
 
         public override bool CanRead
@@ -93,126 +77,70 @@ namespace Microsoft.AspNetCore.TestHost
 
         public override void Flush()
         {
+            FlushAsync().GetAwaiter().GetResult();
+        }
+
+        public override async Task FlushAsync(CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
             CheckNotComplete();
 
-            _writeLock.Wait();
+            await _writeLock.WaitAsync(cancellationToken);
             try
             {
-                FirstWriteAsync().GetAwaiter().GetResult();
+                await FirstWriteAsync();
+                await _pipe.Writer.FlushAsync(cancellationToken);
             }
             finally
             {
                 _writeLock.Release();
             }
-
-            // TODO: Wait for data to drain?
-        }
-
-        public override Task FlushAsync(CancellationToken cancellationToken)
-        {
-            if (cancellationToken.IsCancellationRequested)
-            {
-                TaskCompletionSource<object> tcs = new TaskCompletionSource<object>();
-                tcs.TrySetCanceled();
-                return tcs.Task;
-            }
-
-            Flush();
-
-            // TODO: Wait for data to drain?
-
-            return Task.FromResult<object>(null);
         }
 
         public override int Read(byte[] buffer, int offset, int count)
         {
-            VerifyBuffer(buffer, offset, count, allowEmpty: false);
-            _readLock.Wait();
-            try
-            {
-                int totalRead = 0;
-                do
-                {
-                    // Don't drain buffered data when signaling an abort.
-                    CheckAborted();
-                    if (_topBuffer.Count <= 0)
-                    {
-                        byte[] topBuffer = null;
-                        while (!_bufferedData.TryDequeue(out topBuffer))
-                        {
-                            if (_complete)
-                            {
-                                CheckAborted();
-                                // Graceful close
-                                return totalRead;
-                            }
-                            WaitForDataAsync().Wait();
-                        }
-                        _topBuffer = new ArraySegment<byte>(topBuffer);
-                    }
-                    int actualCount = Math.Min(count, _topBuffer.Count);
-                    Buffer.BlockCopy(_topBuffer.Array, _topBuffer.Offset, buffer, offset, actualCount);
-                    _topBuffer = new ArraySegment<byte>(_topBuffer.Array,
-                        _topBuffer.Offset + actualCount,
-                        _topBuffer.Count - actualCount);
-                    totalRead += actualCount;
-                    offset += actualCount;
-                    count -= actualCount;
-                }
-                while (count > 0 && (_topBuffer.Count > 0 || _bufferedData.Count > 0));
-                // Keep reading while there is more data available and we have more space to put it in.
-                return totalRead;
-            }
-            finally
-            {
-                _readLock.Release();
-            }
+            return ReadAsync(buffer, offset, count, CancellationToken.None).GetAwaiter().GetResult();
         }
 
         public async override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
             VerifyBuffer(buffer, offset, count, allowEmpty: false);
-            CancellationTokenRegistration registration = cancellationToken.Register(Abort);
-            await _readLock.WaitAsync(cancellationToken);
+            CheckAborted();
+            var registration = cancellationToken.Register(Cancel);
             try
             {
-                int totalRead = 0;
-                do
+                // TODO: Usability issue. dotnet/corefx#27732 Flush or zero byte write causes ReadAsync to complete without data so I have to call ReadAsync in a loop.
+                while (true)
                 {
-                    // Don't drained buffered data on abort.
-                    CheckAborted();
-                    if (_topBuffer.Count <= 0)
+                    var result = await _pipe.Reader.ReadAsync(cancellationToken);
+
+                    var readableBuffer = result.Buffer;
+                    if (!readableBuffer.IsEmpty)
                     {
-                        byte[] topBuffer = null;
-                        while (!_bufferedData.TryDequeue(out topBuffer))
-                        {
-                            if (_complete)
-                            {
-                                CheckAborted();
-                                // Graceful close
-                                return totalRead;
-                            }
-                            await WaitForDataAsync();
-                        }
-                        _topBuffer = new ArraySegment<byte>(topBuffer);
+                        var actual = Math.Min(readableBuffer.Length, count);
+                        readableBuffer = readableBuffer.Slice(0, actual);
+                        readableBuffer.CopyTo(new Span<byte>(buffer, offset, count));
+                        _pipe.Reader.AdvanceTo(readableBuffer.End, readableBuffer.End);
+                        return (int)actual;
                     }
-                    int actualCount = Math.Min(count, _topBuffer.Count);
-                    Buffer.BlockCopy(_topBuffer.Array, _topBuffer.Offset, buffer, offset, actualCount);
-                    _topBuffer = new ArraySegment<byte>(_topBuffer.Array,
-                        _topBuffer.Offset + actualCount,
-                        _topBuffer.Count - actualCount);
-                    totalRead += actualCount;
-                    offset += actualCount;
-                    count -= actualCount;
+
+                    if (result.IsCompleted)
+                    {
+                        _pipe.Reader.AdvanceTo(readableBuffer.End, readableBuffer.End); // TODO: Remove after https://github.com/dotnet/corefx/pull/27596
+                        _pipe.Reader.Complete();
+                        return 0;
+                    }
+
+                    cancellationToken.ThrowIfCancellationRequested();
+                    Debug.Assert(!result.IsCanceled); // It should only be canceled by cancellationToken.
+
+                    // Try again. TODO: dotnet/corefx#27732 I shouldn't need to do this, there wasn't any data.
+                    _pipe.Reader.AdvanceTo(readableBuffer.End, readableBuffer.End);
                 }
-                while (count > 0 && (_topBuffer.Count > 0 || _bufferedData.Count > 0));
-                // Keep reading while there is more data available and we have more space to put it in.
-                return totalRead;
             }
             finally
             {
                 registration.Dispose();
-                _readLock.Release();
             }
         }
 
@@ -229,24 +157,21 @@ namespace Microsoft.AspNetCore.TestHost
 
         // Write with count 0 will still trigger OnFirstWrite
         public override void Write(byte[] buffer, int offset, int count)
+        {
+            // The Pipe Write method requires calling FlushAsync to notify the reader. Call WriteAsync instead.
+            WriteAsync(buffer, offset, count).GetAwaiter().GetResult();
+        }
+
+        public override async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
             VerifyBuffer(buffer, offset, count, allowEmpty: true);
             CheckNotComplete();
 
-            _writeLock.Wait();
+            await _writeLock.WaitAsync(cancellationToken);
             try
             {
-                FirstWriteAsync().GetAwaiter().GetResult();
-                if (count == 0)
-                {
-                    return;
-                }
-                // Copies are necessary because we don't know what the caller is going to do with the buffer afterwards.
-                byte[] internalBuffer = new byte[count];
-                Buffer.BlockCopy(buffer, offset, internalBuffer, 0, count);
-                _bufferedData.Enqueue(internalBuffer);
-
-                SignalDataAvailable();
+                await FirstWriteAsync();
+                await _pipe.Writer.WriteAsync(new ReadOnlyMemory<byte>(buffer, offset, count), cancellationToken);
             }
             finally
             {
@@ -254,37 +179,6 @@ namespace Microsoft.AspNetCore.TestHost
             }
         }
 
-        public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
-        {
-            Write(buffer, offset, count);
-            TaskCompletionSource<object> tcs = new TaskCompletionSource<object>(state);
-            tcs.TrySetResult(null);
-            IAsyncResult result = tcs.Task;
-            if (callback != null)
-            {
-                callback(result);
-            }
-            return result;
-        }
-
-        public override void EndWrite(IAsyncResult asyncResult)
-        {
-        }
-
-        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
-        {
-            VerifyBuffer(buffer, offset, count, allowEmpty: true);
-            if (cancellationToken.IsCancellationRequested)
-            {
-                TaskCompletionSource<object> tcs = new TaskCompletionSource<object>();
-                tcs.TrySetCanceled();
-                return tcs.Task;
-            }
-
-            Write(buffer, offset, count);
-            return Task.FromResult<object>(null);
-        }
-
         private static void VerifyBuffer(byte[] buffer, int offset, int count, bool allowEmpty)
         {
             if (buffer == null)
@@ -302,32 +196,12 @@ namespace Microsoft.AspNetCore.TestHost
             }
         }
 
-        private void SignalDataAvailable()
+        internal void Cancel()
         {
-            // Dispatch, as TrySetResult will synchronously execute the waiters callback and block our Write.
-            Task.Factory.StartNew(() => _readWaitingForData.TrySetResult(null));
-        }
-
-        private Task WaitForDataAsync()
-        {
-            // Prevent race with Dispose
-            lock (_signalReadLock)
-            {
-                _readWaitingForData = new TaskCompletionSource<object>();
-
-                if (!_bufferedData.IsEmpty || _complete)
-                {
-                    // Race, data could have arrived before we created the TCS.
-                    _readWaitingForData.TrySetResult(null);
-                }
-
-                return _readWaitingForData.Task;
-            }
-        }
-
-        internal void Abort()
-        {
-            Abort(new OperationCanceledException());
+            _aborted = true;
+            _abortException = new OperationCanceledException();
+            _complete = true;
+            _pipe.Writer.Complete(_abortException);
         }
 
         internal void Abort(Exception innerException)
@@ -335,10 +209,11 @@ namespace Microsoft.AspNetCore.TestHost
             Contract.Requires(innerException != null);
             _aborted = true;
             _abortException = innerException;
-            Complete();
+            _complete = true;
+            _pipe.Writer.Complete(new IOException(string.Empty, innerException));
         }
 
-        internal void Complete()
+        internal void CompleteWrites()
         {
             // If HttpClient.Dispose gets called while HttpClient.SetTask...() is called
             // there is a chance that this method will be called twice and hang on the lock
@@ -348,13 +223,9 @@ namespace Microsoft.AspNetCore.TestHost
                 return;
             }
 
-            // Prevent race with WaitForDataAsync
-            lock (_signalReadLock)
-            {
-                // Throw for further writes, but not reads.  Allow reads to drain the buffered data and then return 0 for further reads.
-                _complete = true;
-                _readWaitingForData.TrySetResult(null);
-            }
+            // Throw for further writes, but not reads.  Allow reads to drain the buffered data and then return 0 for further reads.
+            _complete = true;
+            _pipe.Writer.Complete();
         }
 
         private void CheckAborted()
diff --git a/test/Microsoft.AspNetCore.TestHost.Tests/ClientHandlerTests.cs b/test/Microsoft.AspNetCore.TestHost.Tests/ClientHandlerTests.cs
index 75250206d0..73f1c86d29 100644
--- a/test/Microsoft.AspNetCore.TestHost.Tests/ClientHandlerTests.cs
+++ b/test/Microsoft.AspNetCore.TestHost.Tests/ClientHandlerTests.cs
@@ -210,8 +210,7 @@ namespace Microsoft.AspNetCore.TestHost
             Task<int> readTask = responseStream.ReadAsync(new byte[100], 0, 100);
             Assert.False(readTask.IsCompleted);
             responseStream.Dispose();
-            Thread.Sleep(50);
-            Assert.True(readTask.IsCompleted);
+            Assert.True(readTask.Wait(TimeSpan.FromSeconds(10)), "Finished");
             Assert.Equal(0, readTask.Result);
             block.Set();
         }
@@ -234,11 +233,10 @@ namespace Microsoft.AspNetCore.TestHost
             Stream responseStream = await response.Content.ReadAsStreamAsync();
             CancellationTokenSource cts = new CancellationTokenSource();
             Task<int> readTask = responseStream.ReadAsync(new byte[100], 0, 100, cts.Token);
-            Assert.False(readTask.IsCompleted);
+            Assert.False(readTask.IsCompleted, "Not Completed");
             cts.Cancel();
-            Thread.Sleep(50);
-            Assert.True(readTask.IsCompleted);
-            Assert.True(readTask.IsFaulted);
+            var ex = Assert.Throws<AggregateException>(() => readTask.Wait(TimeSpan.FromSeconds(10)));
+            Assert.IsAssignableFrom<OperationCanceledException>(ex.GetBaseException());
             block.Set();
         }
 
diff --git a/test/Microsoft.AspNetCore.TestHost.Tests/HttpContextBuilderTests.cs b/test/Microsoft.AspNetCore.TestHost.Tests/HttpContextBuilderTests.cs
index e7744ef449..21539c8988 100644
--- a/test/Microsoft.AspNetCore.TestHost.Tests/HttpContextBuilderTests.cs
+++ b/test/Microsoft.AspNetCore.TestHost.Tests/HttpContextBuilderTests.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
@@ -99,7 +100,34 @@ namespace Microsoft.AspNetCore.TestHost
         }
 
         [Fact]
-        public async Task HeadersAvailableBeforeBodyFinished()
+        public async Task HeadersAvailableBeforeSyncBodyFinished()
+        {
+            var block = new ManualResetEvent(false);
+            var builder = new WebHostBuilder().Configure(app =>
+            {
+                app.Run(c =>
+                {
+                    c.Response.Headers["TestHeader"] = "TestValue";
+                    var bytes = Encoding.UTF8.GetBytes("BodyStarted" + Environment.NewLine);
+                    c.Response.Body.Write(bytes, 0, bytes.Length);
+                    Assert.True(block.WaitOne(TimeSpan.FromSeconds(5)));
+                    bytes = Encoding.UTF8.GetBytes("BodyFinished");
+                    c.Response.Body.Write(bytes, 0, bytes.Length);
+                    return Task.CompletedTask;
+                });
+            });
+            var server = new TestServer(builder);
+            var context = await server.SendAsync(c => { });
+
+            Assert.Equal("TestValue", context.Response.Headers["TestHeader"]);
+            var reader = new StreamReader(context.Response.Body);
+            Assert.Equal("BodyStarted", reader.ReadLine());
+            block.Set();
+            Assert.Equal("BodyFinished", reader.ReadToEnd());
+        }
+
+        [Fact]
+        public async Task HeadersAvailableBeforeAsyncBodyFinished()
         {
             var block = new ManualResetEvent(false);
             var builder = new WebHostBuilder().Configure(app =>
@@ -107,8 +135,8 @@ namespace Microsoft.AspNetCore.TestHost
                 app.Run(async c =>
                 {
                     c.Response.Headers["TestHeader"] = "TestValue";
-                    await c.Response.WriteAsync("BodyStarted,");
-                    block.WaitOne();
+                    await c.Response.WriteAsync("BodyStarted" + Environment.NewLine);
+                    Assert.True(block.WaitOne(TimeSpan.FromSeconds(5)));
                     await c.Response.WriteAsync("BodyFinished");
                 });
             });
@@ -116,8 +144,10 @@ namespace Microsoft.AspNetCore.TestHost
             var context = await server.SendAsync(c => { });
 
             Assert.Equal("TestValue", context.Response.Headers["TestHeader"]);
+            var reader = new StreamReader(context.Response.Body);
+            Assert.Equal("BodyStarted", await reader.ReadLineAsync());
             block.Set();
-            Assert.Equal("BodyStarted,BodyFinished", new StreamReader(context.Response.Body).ReadToEnd());
+            Assert.Equal("BodyFinished", await reader.ReadToEndAsync());
         }
 
         [Fact]
@@ -217,7 +247,7 @@ namespace Microsoft.AspNetCore.TestHost
             Assert.False(readTask.IsCompleted);
             cts.Cancel();
             var ex = Assert.Throws<AggregateException>(() => readTask.Wait(TimeSpan.FromSeconds(10)));
-            Assert.IsAssignableFrom<OperationCanceledException>(ex.GetBaseException().InnerException);
+            Assert.IsAssignableFrom<OperationCanceledException>(ex.GetBaseException());
             block.Set();
         }
 
diff --git a/test/Microsoft.AspNetCore.TestHost.Tests/TestClientTests.cs b/test/Microsoft.AspNetCore.TestHost.Tests/TestClientTests.cs
index 6f1d9098bd..3101c2965f 100644
--- a/test/Microsoft.AspNetCore.TestHost.Tests/TestClientTests.cs
+++ b/test/Microsoft.AspNetCore.TestHost.Tests/TestClientTests.cs
@@ -246,7 +246,7 @@ namespace Microsoft.AspNetCore.TestHost
                     var receiveArray = new byte[1024];
                     while (true)
                     {
-                        var receiveResult = await websocket.ReceiveAsync(new System.ArraySegment<byte>(receiveArray), CancellationToken.None);
+                        var receiveResult = await websocket.ReceiveAsync(new ArraySegment<byte>(receiveArray), CancellationToken.None);
                         if (receiveResult.MessageType == WebSocketMessageType.Close)
                         {
                             await websocket.CloseAsync(WebSocketCloseStatus.NormalClosure, "Normal Closure", CancellationToken.None);