diff --git a/src/Tasks.UnitTests/WriteCodeFragment_Tests.cs b/src/Tasks.UnitTests/WriteCodeFragment_Tests.cs
index 22f43163eb1..e72f97b3fbd 100644
--- a/src/Tasks.UnitTests/WriteCodeFragment_Tests.cs
+++ b/src/Tasks.UnitTests/WriteCodeFragment_Tests.cs
@@ -5,6 +5,7 @@
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
+using Microsoft.Build.Framework;
 using Microsoft.Build.Shared;
 using Microsoft.Build.Tasks;
 using Microsoft.Build.Utilities;
@@ -27,6 +28,7 @@ public class WriteCodeFragment_Tests
         public void InvalidLanguage()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "xx";
@@ -44,6 +46,7 @@ public void InvalidLanguage()
         public void NoLanguage()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.OutputFile = new TaskItem("foo");
@@ -60,6 +63,7 @@ public void NoLanguage()
         public void NoFileOrDirectory()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -76,6 +80,7 @@ public void NoFileOrDirectory()
         public void CombineFileDirectory()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -145,6 +150,7 @@ public void FileNameNoDirectory()
             using TestEnvironment env = TestEnvironment.Create();
             var file = env.ExpectFile(Directory.GetCurrentDirectory(), ".tmp");
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -167,6 +173,7 @@ public void FileNameNoDirectory()
         public void DirectoryAndRootedFile()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -202,6 +209,7 @@ public void NoAttributesShouldEmitNoFile()
             }
 
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -229,6 +237,7 @@ public void NoAttributesShouldEmitNoFile2()
             }
 
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -248,6 +257,7 @@ public void NoAttributesShouldEmitNoFile2()
         public void InvalidFilePath()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -266,6 +276,7 @@ public void InvalidFilePath()
         public void InvalidDirectoryPath()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             task.Language = "c#";
@@ -288,6 +299,7 @@ public void OneAttributeNoParams()
             try
             {
                 WriteCodeFragment task = new WriteCodeFragment();
+                task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
                 MockEngine engine = new MockEngine(true);
                 task.BuildEngine = engine;
                 TaskItem attribute = new TaskItem("System.AssemblyTrademarkAttribute");
@@ -317,6 +329,7 @@ public void OneAttributeNoParams()
         public void OneAttributeNoParamsVb()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("System.AssemblyTrademarkAttribute");
@@ -340,6 +353,7 @@ public void OneAttributeNoParamsVb()
         public void TwoAttributes()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute1 = new TaskItem("AssemblyTrademarkAttribute");
@@ -369,6 +383,7 @@ public void TwoAttributes()
         public void ToDirectory()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("System.AssemblyTrademarkAttribute");
@@ -406,6 +421,55 @@ public void ToDirectoryAndDirectoryDoesNotExist()
             Assert.Equal(".cs", task.OutputFile.ItemSpec.Substring(task.OutputFile.ItemSpec.Length - 3));
         }
 
+        /// <summary>
+        /// When OutputDirectory is relative and OutputFile is not specified, the resulting OutputFile should be relative.
+        /// </summary>
+        [Fact]
+        public void RelativeOutputDirectoryProducesRelativeOutputFile()
+        {
+            using TestEnvironment env = TestEnvironment.Create();
+
+            // Create an actual folder and get a relative path to it
+            string absoluteFolder = env.CreateFolder().Path;
+            string relativeFolder = Path.GetFileName(absoluteFolder);
+
+            // Change current directory to the parent so the relative path works
+            string originalDir = Directory.GetCurrentDirectory();
+            try
+            {
+                Directory.SetCurrentDirectory(Path.GetDirectoryName(absoluteFolder));
+
+                WriteCodeFragment task = new WriteCodeFragment();
+                task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
+                MockEngine engine = new MockEngine(true);
+                task.BuildEngine = engine;
+                TaskItem attribute = new TaskItem("System.AssemblyTrademarkAttribute");
+                task.AssemblyAttributes = new TaskItem[] { attribute };
+                task.Language = "c#";
+                task.OutputDirectory = new TaskItem(relativeFolder);
+                bool result = task.Execute();
+
+                result.ShouldBeTrue(engine.Log);
+
+                // The output file should be relative (not rooted) since OutputDirectory was relative
+                Path.IsPathRooted(task.OutputFile.ItemSpec).ShouldBeFalse("OutputFile should be relative when OutputDirectory is relative");
+
+                // The output file should start with the relative folder name
+                task.OutputFile.ItemSpec.ShouldStartWith(relativeFolder);
+
+                // Cleanup the generated file
+                string absoluteOutputFile = Path.Combine(Path.GetDirectoryName(absoluteFolder), task.OutputFile.ItemSpec);
+                if (File.Exists(absoluteOutputFile))
+                {
+                    File.Delete(absoluteOutputFile);
+                }
+            }
+            finally
+            {
+                Directory.SetCurrentDirectory(originalDir);
+            }
+        }
+
         /// <summary>
         /// Regular case
         /// </summary>
@@ -417,6 +481,7 @@ public void OneAttributeTwoParams()
             try
             {
                 WriteCodeFragment task = new WriteCodeFragment();
+                task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
                 MockEngine engine = new MockEngine(true);
                 task.BuildEngine = engine;
                 TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -448,6 +513,7 @@ public void OneAttributeTwoParams()
         public void OneAttributeTwoParamsSameName()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -471,6 +537,7 @@ public void OneAttributeTwoParamsSameName()
         public void OneAttributePositionalParamInvalidSuffix()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -494,6 +561,7 @@ public void OneAttributePositionalParamInvalidSuffix()
         public void OneAttributeTwoPositionalParams()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -518,6 +586,7 @@ public void OneAttributeTwoPositionalParams()
         public void OneAttributeTwoPositionalParamsWithSameValue()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyMetadataAttribute");
@@ -550,6 +619,7 @@ public void MultilineAttributeCSharp()
             var multilineString = String.Join(Environment.NewLine, lines);
 
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("System.Reflection.AssemblyDescriptionAttribute");
@@ -586,6 +656,7 @@ public void MultilineAttributeVB()
             var multilineString = String.Join(Environment.NewLine, lines);
 
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("System.Reflection.AssemblyDescriptionAttribute");
@@ -619,6 +690,7 @@ public void MultilineAttributeVB()
         public void OneAttributeSkippedPositionalParams()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -642,6 +714,7 @@ public void OneAttributeSkippedPositionalParams()
         public void InvalidNumber()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -665,6 +738,7 @@ public void InvalidNumber()
         public void NoNumber()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -688,6 +762,7 @@ public void NoNumber()
         public void OneAttributePositionalAndNamedParams()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -721,6 +796,7 @@ public void OneAttributePositionalAndNamedParams()
         public void OneAttributePositionalAndNamedParamsVisualBasic()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("AssemblyTrademarkAttribute");
@@ -1062,6 +1138,7 @@ public void InferredTypeFallsBackToStringWhenTypeConversionFails()
         public void MessageDisplayPositionalParameterNameWhenAttributeNotFound()
         {
             WriteCodeFragment task = new WriteCodeFragment();
+            task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
             MockEngine engine = new MockEngine(true);
             task.BuildEngine = engine;
             TaskItem attribute = new TaskItem("System.TheAttributeCannotFound");
@@ -1101,6 +1178,7 @@ private WriteCodeFragment CreateTask(string language, TaskItem outputDirectory,
         {
             return new WriteCodeFragment()
             {
+                TaskEnvironment = TaskEnvironmentHelper.CreateForTest(),
                 Language = language,
                 OutputDirectory = outputDirectory,
                 OutputFile = outputFile,
@@ -1218,6 +1296,7 @@ public void CommentIsInvariantCulture(string cultureName)
                 System.Globalization.CultureInfo.CurrentUICulture = new System.Globalization.CultureInfo(cultureName);
                 
                 WriteCodeFragment task = new WriteCodeFragment();
+                task.TaskEnvironment = TaskEnvironmentHelper.CreateForTest();
                 MockEngine engine = new MockEngine(true);
                 task.BuildEngine = engine;
                 TaskItem attribute = new TaskItem("System.AssemblyVersionAttribute");
diff --git a/src/Tasks/WriteCodeFragment.cs b/src/Tasks/WriteCodeFragment.cs
index cf3d673835f..c0f58314d0f 100644
--- a/src/Tasks/WriteCodeFragment.cs
+++ b/src/Tasks/WriteCodeFragment.cs
@@ -30,8 +30,11 @@ namespace Microsoft.Build.Tasks
     /// <comment>
     /// Currently only supports writing .NET attributes.
     /// </comment>
-    public class WriteCodeFragment : TaskExtension
+    [MSBuildMultiThreadableTask]
+    public class WriteCodeFragment : TaskExtension, IMultiThreadableTask
     {
+        /// <inheritdoc />
+        public TaskEnvironment TaskEnvironment { get; set; }
         private const string TypeNameSuffix = "_TypeName";
         private const string IsLiteralSuffix = "_IsLiteral";
         private static readonly string[] NamespaceImports = ["System", "System.Reflection"];
@@ -104,6 +107,7 @@ public override bool Execute()
                 return true;
             }
 
+            AbsolutePath outputFilePath = default;
             try
             {
                 if (OutputFile != null && OutputDirectory != null && !Path.IsPathRooted(OutputFile.ItemSpec))
@@ -111,16 +115,25 @@ public override bool Execute()
                     OutputFile = new TaskItem(Path.Combine(OutputDirectory.ItemSpec, OutputFile.ItemSpec));
                 }
 
-                OutputFile ??= new TaskItem(FileUtilities.GetTemporaryFile(OutputDirectory.ItemSpec, null, extension));
+                if (OutputFile != null)
+                {
+                    outputFilePath = TaskEnvironment.GetAbsolutePath(OutputFile.ItemSpec);
+                }
+                else
+                {
+                    AbsolutePath outputDirectoryPath = TaskEnvironment.GetAbsolutePath(OutputDirectory.ItemSpec);
+                    outputFilePath = new AbsolutePath(FileUtilities.GetTemporaryFile(outputDirectoryPath, null, extension));
+                    OutputFile = new TaskItem(Path.Combine(OutputDirectory.ItemSpec, Path.GetFileName(outputFilePath.Value)));
+                }
 
-                FileUtilities.EnsureDirectoryExists(Path.GetDirectoryName(OutputFile.ItemSpec));
+                FileUtilities.EnsureDirectoryExists(Path.GetDirectoryName(outputFilePath));
 
-                File.WriteAllText(OutputFile.ItemSpec, code); // Overwrites file if it already exists (and can be overwritten)
+                File.WriteAllText(outputFilePath, code); // Overwrites file if it already exists (and can be overwritten)
             }
             catch (Exception ex) when (ExceptionHandling.IsIoRelatedException(ex))
             {
                 string itemSpec = OutputFile?.ItemSpec ?? String.Empty;
-                string lockedFileMessage = LockCheck.GetLockedFileMessage(itemSpec);
+                string lockedFileMessage = LockCheck.GetLockedFileMessage(outputFilePath.Value ?? itemSpec);
                 Log.LogErrorWithCodeFromResources("WriteCodeFragment.CouldNotWriteOutput", itemSpec, ex.Message, lockedFileMessage);
                 return false;
             }