diff --git a/src/TestFramework/TestFramework/Assertions/Assert.AreAllDistinct.cs b/src/TestFramework/TestFramework/Assertions/Assert.AreAllDistinct.cs
index 0b26bc2f03..769c27ced2 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.AreAllDistinct.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.AreAllDistinct.cs
@@ -222,8 +222,8 @@ private static void ReportAssertAreAllDistinctFailed<T>(IEnumerable<T> collectio
 
     #endregion // AreAllDistinct
 
-    // TODO: Deduplicate with the same adapter in Assert.CollectionEquivalence.cs (introduced by PR #8234)
-    // once both PRs have landed.
+    // Adapts a non-generic IEqualityComparer to IEqualityComparer<object?> for assertion helpers.
+    [StackTraceHidden]
     private sealed class NonGenericEqualityComparerAdapter : IEqualityComparer<object?>
     {
         private readonly IEqualityComparer _comparer;
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.AreAllOfType.cs b/src/TestFramework/TestFramework/Assertions/Assert.AreAllOfType.cs
index 7b1cce4427..2f4037edae 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.AreAllOfType.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.AreAllOfType.cs
@@ -159,6 +159,7 @@ private static void ReportAssertAreAllOfTypeFailed(IEnumerable<object?> collecti
         ReportAssertFailed(structured);
     }
 
+    [StackTraceHidden]
     private readonly struct TypeMismatch
     {
         public TypeMismatch(int index, Type? actualType)
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Comparer.cs b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Comparer.cs
index 004c7e4222..01e856742a 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Comparer.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Comparer.cs
@@ -8,6 +8,7 @@ public sealed partial class Assert
     /// <summary>
     /// Walks two object graphs and reports the first structural difference, if any.
     /// </summary>
+    [StackTraceHidden]
     private sealed partial class EquivalenceComparer
     {
         // Member info caches keyed by runtime type.
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.DictionaryView.cs b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.DictionaryView.cs
index dcb3eec99a..41b40c7820 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.DictionaryView.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.DictionaryView.cs
@@ -11,6 +11,7 @@ public sealed partial class Assert
     /// Routes lookups back to the source dictionary so the source's own
     /// <see cref="IEqualityComparer{T}"/> for keys is preserved.
     /// </summary>
+    [StackTraceHidden]
     private abstract class DictionaryView
     {
         internal abstract IEnumerable<KeyValuePair<object, object?>> Entries { get; }
@@ -30,6 +31,7 @@ internal DictionaryLookup TryGetValuePair(object key)
         }
     }
 
+    [StackTraceHidden]
     private readonly struct DictionaryLookup
     {
         internal DictionaryLookup(bool found, object? value)
@@ -43,6 +45,7 @@ internal DictionaryLookup(bool found, object? value)
         internal object? Value { get; }
     }
 
+    [StackTraceHidden]
     private sealed class NonGenericDictionaryView : DictionaryView
     {
         private readonly IDictionary _source;
@@ -84,6 +87,7 @@ internal override bool TryGetValue(object key, out object? value)
         }
     }
 
+    [StackTraceHidden]
     private sealed class GenericDictionaryView : DictionaryView
     {
         private static readonly ConcurrentDictionary<Type, GenericDictionaryAccessors> AccessorCache = new();
@@ -123,6 +127,7 @@ internal override bool TryGetValue(object key, out object? value)
     /// source's native methods (<c>TryGetValue</c>, <c>ContainsKey</c>) so the source's
     /// <see cref="IEqualityComparer{TKey}"/> is honored.
     /// </summary>
+    [StackTraceHidden]
     private sealed class GenericDictionaryAccessors
     {
         private readonly MethodInfo _tryGetValueMethod;
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.MemberAccessor.cs b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.MemberAccessor.cs
index 737d44fb32..896a114645 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.MemberAccessor.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.MemberAccessor.cs
@@ -8,6 +8,7 @@ public sealed partial class Assert
     /// <summary>
     /// Reference-equality comparer used for keys in the topology maps of <see cref="EquivalenceComparer"/>.
     /// </summary>
+    [StackTraceHidden]
     private sealed class ReferenceObjectComparer : IEqualityComparer<object>
     {
         internal static readonly ReferenceObjectComparer Instance = new();
@@ -25,6 +26,7 @@ private ReferenceObjectComparer()
     /// Cached set of public instance properties and fields for a type, with both an alphabetically-sorted
     /// array (for deterministic traversal) and a name-keyed dictionary (for O(1) lookup).
     /// </summary>
+    [StackTraceHidden]
     private sealed class MemberLookup
     {
         internal MemberLookup(MemberAccessor[] sorted, IReadOnlyDictionary<string, MemberAccessor> byName)
@@ -41,6 +43,7 @@ internal MemberLookup(MemberAccessor[] sorted, IReadOnlyDictionary<string, Membe
     /// <summary>
     /// Describes how to read a single member (property or field) from an instance.
     /// </summary>
+    [StackTraceHidden]
     private sealed class MemberAccessor
     {
         private readonly PropertyInfo? _property;
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Mismatch.cs b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Mismatch.cs
index 24703874d4..2ef4142618 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Mismatch.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.AreEquivalent.Mismatch.cs
@@ -9,6 +9,7 @@ public sealed partial class Assert
     /// A single structural mismatch found by <see cref="EquivalenceComparer"/>, carrying the dotted
     /// member path, a localized reason summary, and any expected/actual snippets to render.
     /// </summary>
+    [StackTraceHidden]
     private sealed class EquivalenceMismatch
     {
         private EquivalenceMismatch(string path, string reason, string? expectedText, string? actualText, bool isComparisonFailure)
diff --git a/src/TestFramework/TestFramework/Assertions/Assert.ThrowsException.cs b/src/TestFramework/TestFramework/Assertions/Assert.ThrowsException.cs
index b2b2c7df98..764f7de791 100644
--- a/src/TestFramework/TestFramework/Assertions/Assert.ThrowsException.cs
+++ b/src/TestFramework/TestFramework/Assertions/Assert.ThrowsException.cs
@@ -674,6 +674,7 @@ private enum ThrowsFailureKind : byte
         WrongExceptionType,
     }
 
+    [StackTraceHidden]
     private readonly struct ThrowsExceptionState
     {
         public Exception? ExceptionThrown { get; }
diff --git a/src/TestFramework/TestFramework/Assertions/CollectionAssert.Helpers.cs b/src/TestFramework/TestFramework/Assertions/CollectionAssert.Helpers.cs
index b23f306c6e..e57e2b3699 100644
--- a/src/TestFramework/TestFramework/Assertions/CollectionAssert.Helpers.cs
+++ b/src/TestFramework/TestFramework/Assertions/CollectionAssert.Helpers.cs
@@ -277,6 +277,7 @@ private static string ConstructFinalMessage(
     /// <summary>
     /// compares the objects using object.Equals.
     /// </summary>
+    [StackTraceHidden]
     private sealed class ObjectComparer : IComparer
     {
         int IComparer.Compare(object? x, object? y) => Equals(x, y) ? 0 : -1;