diff --git a/src/Adapter/MSTest.TestAdapter/MSTest.TestAdapter.csproj b/src/Adapter/MSTest.TestAdapter/MSTest.TestAdapter.csproj
index b4792d9cad..23655fc099 100644
--- a/src/Adapter/MSTest.TestAdapter/MSTest.TestAdapter.csproj
+++ b/src/Adapter/MSTest.TestAdapter/MSTest.TestAdapter.csproj
@@ -82,6 +82,12 @@
          that reference is suppressed above, so they are referenced explicitly here. -->
     <PackageReference Include="System.Threading.Tasks.Extensions" Condition=" '$(TargetFramework)' == '$(NetFrameworkMinimum)' OR '$(TargetFramework)' == '$(UwpMinimum)' " />
     <PackageReference Include="System.Memory" Condition=" '$(TargetFramework)' == '$(NetFrameworkMinimum)' OR '$(TargetFramework)' == '$(UwpMinimum)' " />
+
+    <!-- The adapter's VSTest-facing code (VSTestAdapter\*, AdapterTestProperties) uses the VSTest object model
+         directly. On other TFMs it flows in transitively via Microsoft.Testing.Extensions.VSTestBridge, but that
+         reference is not added for UWP (see above), and PlatformServices no longer references the object model,
+         so it is referenced explicitly here for UWP. -->
+    <PackageReference Include="Microsoft.TestPlatform.ObjectModel" Condition=" '$(TargetFramework)' == '$(UwpMinimum)' " />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/Adapter/MSTestAdapter.PlatformServices/ApartmentStateSetting.cs b/src/Adapter/MSTestAdapter.PlatformServices/ApartmentStateSetting.cs
new file mode 100644
index 0000000000..4bb4f09f3a
--- /dev/null
+++ b/src/Adapter/MSTestAdapter.PlatformServices/ApartmentStateSetting.cs
@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter;
+
+/// <summary>
+/// Apartment state parsed from the <c>ExecutionThreadApartmentState</c> run settings and the
+/// <c>mstest:execution:executionApartmentState</c> configuration value. This is the adapter's own neutral
+/// replacement for the former VSTest <c>PlatformAbstractions.PlatformApartmentState</c> enum.
+/// </summary>
+internal enum ApartmentStateSetting
+{
+    // The member order is load-bearing: Enum.TryParse maps numeric-string run settings values ("0"/"1")
+    // by number, so MTA must stay 0 and STA must stay 1 to preserve parse compatibility with the former
+    // VSTest PlatformAbstractions.PlatformApartmentState enum. Do not reorder.
+    MTA,
+    STA,
+}
diff --git a/src/Adapter/MSTestAdapter.PlatformServices/MSTestAdapter.PlatformServices.csproj b/src/Adapter/MSTestAdapter.PlatformServices/MSTestAdapter.PlatformServices.csproj
index 6a9e8820b1..97813d16d1 100644
--- a/src/Adapter/MSTestAdapter.PlatformServices/MSTestAdapter.PlatformServices.csproj
+++ b/src/Adapter/MSTestAdapter.PlatformServices/MSTestAdapter.PlatformServices.csproj
@@ -36,7 +36,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.TestPlatform.ObjectModel" />
     <PackageReference Include="System.Threading.Tasks.Extensions" Condition=" '$(TargetFramework)' == 'netstandard2.0' OR '$(TargetFramework)' == '$(NetFrameworkMinimum)' OR '$(TargetFramework)' == '$(UwpMinimum)' " />
     <!-- Span/MemoryMarshal used by the linked XxHash code below live in System.Memory on these TFMs.
          Referenced explicitly so the compiled assembly binds the System.Memory assembly version 4.0.5.0
@@ -44,6 +43,13 @@
     <PackageReference Include="System.Memory" Condition=" '$(TargetFramework)' == 'netstandard2.0' OR '$(TargetFramework)' == '$(NetFrameworkMinimum)' OR '$(TargetFramework)' == '$(UwpMinimum)' " />
   </ItemGroup>
 
+  <!-- System.Configuration (ConfigurationManager / ConfigurationElementCollection used by TestDataSource on .NET
+       Framework) was previously pulled in transitively via Microsoft.TestPlatform.ObjectModel. It is a framework
+       assembly, so it is referenced directly now that the object-model package reference is removed. -->
+  <ItemGroup Condition=" '$(TargetFramework)' == '$(NetFrameworkMinimum)' ">
+    <Reference Include="System.Configuration" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Include="$(RepoRoot)src/Polyfills/**/*.cs" Link="Polyfills\%(RecursiveDir)%(Filename)%(Extension)" />
   </ItemGroup>
diff --git a/src/Adapter/MSTestAdapter.PlatformServices/RunConfigurationSettings.cs b/src/Adapter/MSTestAdapter.PlatformServices/RunConfigurationSettings.cs
index 5723c35a44..8423ab05b6 100644
--- a/src/Adapter/MSTestAdapter.PlatformServices/RunConfigurationSettings.cs
+++ b/src/Adapter/MSTestAdapter.PlatformServices/RunConfigurationSettings.cs
@@ -5,7 +5,6 @@
 using Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.Interface;
 #endif
 
-using Microsoft.VisualStudio.TestPlatform.PlatformAbstractions;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter;
@@ -96,13 +95,13 @@ private static RunConfigurationSettings ToSettings(XmlReader reader)
                 {
                     case "EXECUTIONTHREADAPARTMENTSTATE":
                         {
-                            if (Enum.TryParse(reader.ReadInnerXml(), out PlatformApartmentState platformApartmentState))
+                            if (Enum.TryParse(reader.ReadInnerXml(), out ApartmentStateSetting apartmentStateSetting))
                             {
-                                settings.ExecutionApartmentState = platformApartmentState switch
+                                settings.ExecutionApartmentState = apartmentStateSetting switch
                                 {
-                                    PlatformApartmentState.STA => ApartmentState.STA,
-                                    PlatformApartmentState.MTA => ApartmentState.MTA,
-                                    _ => throw new NotSupportedException($"Platform apartment state '{platformApartmentState}' is not supported."),
+                                    ApartmentStateSetting.STA => ApartmentState.STA,
+                                    ApartmentStateSetting.MTA => ApartmentState.MTA,
+                                    _ => throw new NotSupportedException($"Platform apartment state '{apartmentStateSetting}' is not supported."),
                                 };
                             }
 
@@ -131,13 +130,13 @@ internal static RunConfigurationSettings SetRunConfigurationSettingsFromConfig(I
         //  }
         // }
         string? apartmentStateValue = configuration["mstest:execution:executionApartmentState"];
-        if (Enum.TryParse(apartmentStateValue, out PlatformApartmentState platformApartmentState))
+        if (Enum.TryParse(apartmentStateValue, out ApartmentStateSetting apartmentStateSetting))
         {
-            settings.ExecutionApartmentState = platformApartmentState switch
+            settings.ExecutionApartmentState = apartmentStateSetting switch
             {
-                PlatformApartmentState.STA => ApartmentState.STA,
-                PlatformApartmentState.MTA => ApartmentState.MTA,
-                _ => throw new NotSupportedException(string.Format(CultureInfo.CurrentCulture, Resource.InvalidValue, platformApartmentState, "execution:executionApartmentState")),
+                ApartmentStateSetting.STA => ApartmentState.STA,
+                ApartmentStateSetting.MTA => ApartmentState.MTA,
+                _ => throw new NotSupportedException(string.Format(CultureInfo.CurrentCulture, Resource.InvalidValue, apartmentStateSetting, "execution:executionApartmentState")),
             };
         }
 
diff --git a/src/Adapter/MSTestAdapter.PlatformServices/Services/TestSourceHandler.cs b/src/Adapter/MSTestAdapter.PlatformServices/Services/TestSourceHandler.cs
index a2ce548535..ae97ba6ab2 100644
--- a/src/Adapter/MSTestAdapter.PlatformServices/Services/TestSourceHandler.cs
+++ b/src/Adapter/MSTestAdapter.PlatformServices/Services/TestSourceHandler.cs
@@ -110,7 +110,7 @@ public bool IsAssemblyReferenced(AssemblyName assemblyName, string source)
         try
         {
             string? referenceAssemblyName = referenceAssembly.Name;
-            byte[] referenceAssemblyPublicKeyToken = referenceAssembly.GetPublicKeyToken();
+            byte[]? referenceAssemblyPublicKeyToken = referenceAssembly.GetPublicKeyToken();
 
             // ReflectionOnlyLoadFrom loads from the specified path only (no probing) and does not
             // execute any code from the loaded assembly.
@@ -139,8 +139,20 @@ public bool IsAssemblyReferenced(AssemblyName assemblyName, string source)
         }
     }
 
-    private static bool ArePublicKeyTokensEqual(byte[] left, byte[] right)
+    private static bool ArePublicKeyTokensEqual(byte[]? left, byte[]? right)
     {
+        // GetPublicKeyToken() returns null (or an empty array) for unsigned assemblies.
+        // Treat two unsigned tokens as equal, and a signed vs. unsigned pair as unequal.
+        if (left is null || left.Length == 0)
+        {
+            return right is null || right.Length == 0;
+        }
+
+        if (right is null || right.Length == 0)
+        {
+            return false;
+        }
+
         if (left.Length != right.Length)
         {
             return false;
diff --git a/test/IntegrationTests/PlatformServices.Desktop.IntegrationTests/PlatformServices.Desktop.IntegrationTests.csproj b/test/IntegrationTests/PlatformServices.Desktop.IntegrationTests/PlatformServices.Desktop.IntegrationTests.csproj
index de991b9157..0f8dac1571 100644
--- a/test/IntegrationTests/PlatformServices.Desktop.IntegrationTests/PlatformServices.Desktop.IntegrationTests.csproj
+++ b/test/IntegrationTests/PlatformServices.Desktop.IntegrationTests/PlatformServices.Desktop.IntegrationTests.csproj
@@ -15,6 +15,9 @@
     <PackageReference Include="Moq" />
     <PackageReference Include="AwesomeAssertions" />
     <PackageReference Include="StrongNamer" />
+    <!-- This test uses ObjectModel's XmlRunSettingsUtilities directly; it was previously provided transitively
+         through the MSTestAdapter.PlatformServices project reference, which no longer depends on the object model. -->
+    <PackageReference Include="Microsoft.TestPlatform.ObjectModel" />
   </ItemGroup>
 
 </Project>
diff --git a/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/ObjectModelDecouplingTests.cs b/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/ObjectModelDecouplingTests.cs
new file mode 100644
index 0000000000..16efa478fc
--- /dev/null
+++ b/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/ObjectModelDecouplingTests.cs
@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using AwesomeAssertions;
+
+using Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices;
+
+using TestFramework.ForTestingMSTest;
+
+namespace MSTestAdapter.PlatformServices.UnitTests;
+
+public class ObjectModelDecouplingTests : TestContainer
+{
+    // Guards the platform-agnostic contract: the compiled MSTestAdapter.PlatformServices assembly must not
+    // reference the VSTest object model (Microsoft.VisualStudio.TestPlatform.ObjectModel) or any other
+    // Microsoft.*.TestPlatform.* assembly. All VSTest coupling lives in the MSTest.TestAdapter layer above it.
+    public void PlatformServicesAssemblyShouldNotReferenceAnyTestPlatformAssembly()
+    {
+        Assembly platformServices = typeof(TestSourceHandler).Assembly;
+
+        IEnumerable<string> testPlatformReferences = platformServices
+            .GetReferencedAssemblies()
+            .Select(reference => reference.Name!)
+            .Where(name => name.IndexOf("TestPlatform", StringComparison.OrdinalIgnoreCase) >= 0);
+
+        testPlatformReferences.Should().BeEmpty(
+            "PlatformServices must stay platform-agnostic and must not reference the VSTest object model or any Microsoft.*.TestPlatform.* assembly");
+    }
+}
diff --git a/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/Services/DesktopTestSourceTests.cs b/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/Services/DesktopTestSourceTests.cs
index 461efbd2dd..2ea65db70a 100644
--- a/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/Services/DesktopTestSourceTests.cs
+++ b/test/UnitTests/MSTestAdapter.PlatformServices.UnitTests/Services/DesktopTestSourceTests.cs
@@ -29,5 +29,20 @@ public class DesktopTestSourceTests : TestContainer
     public void IsAssemblyReferencedShouldReturnTrueIfAnAssemblyIsReferencedInSource() => _testSource.IsAssemblyReferenced(typeof(Microsoft.VisualStudio.TestTools.UnitTesting.TestMethodAttribute).Assembly.GetName(), Assembly.GetExecutingAssembly().Location).Should().BeTrue();
 
     public void IsAssemblyReferencedShouldReturnFalseIfAnAssemblyIsNotReferencedInSource() => _testSource.IsAssemblyReferenced(new AssemblyName("foobar"), Assembly.GetExecutingAssembly().Location).Should().BeFalse();
+
+    // The source references the strong-named MSTest.TestFramework assembly. Passing an assembly name with the
+    // same simple name but no public key token (as an unsigned build would have) must not be considered a match:
+    // the public key tokens differ (signed vs. unsigned), so IsAssemblyReferenced returns false. This guards the
+    // signed-vs-unsigned branch of the public-key-token comparison.
+    public void IsAssemblyReferencedShouldReturnFalseIfPublicKeyTokenIsMissing() => _testSource.IsAssemblyReferenced(new AssemblyName("MSTest.TestFramework"), Assembly.GetExecutingAssembly().Location).Should().BeFalse();
+
+    // Same simple name but a different (non-null) public key token must also not match: the tokens are compared
+    // byte-by-byte and differ. This guards the differing-token branch of the public-key-token comparison.
+    public void IsAssemblyReferencedShouldReturnFalseIfPublicKeyTokenDiffers()
+    {
+        var assemblyName = new AssemblyName("MSTest.TestFramework");
+        assemblyName.SetPublicKeyToken([0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08]);
+        _testSource.IsAssemblyReferenced(assemblyName, Assembly.GetExecutingAssembly().Location).Should().BeFalse();
+    }
 }
 #endif