diff --git a/src/DynamicData.Tests/Domain/Animal.cs b/src/DynamicData.Tests/Domain/Animal.cs
index 983cde9a5..b97f6a6ee 100644
--- a/src/DynamicData.Tests/Domain/Animal.cs
+++ b/src/DynamicData.Tests/Domain/Animal.cs
@@ -19,7 +19,7 @@ public enum AnimalFamily
     Bird
 }
 
-public class Animal(string name, string type, AnimalFamily family, bool include = true, int? id = null) : AbstractNotifyPropertyChanged
+public sealed class Animal(string name, string type, AnimalFamily family, bool include = true, int? id = null) : AbstractNotifyPropertyChanged
 {
     private static int s_counter;
 
@@ -46,7 +46,7 @@ public bool IncludeInResults
     public override int GetHashCode() => HashCode.Combine(Id, Name, Family, Type);
 }
 
-public class AnimalEqualityComparer : IEqualityComparer<Animal>
+public sealed class AnimalEqualityComparer : IEqualityComparer<Animal>
 {
     public static AnimalEqualityComparer Instance { get; } = new();
 
diff --git a/src/DynamicData.Tests/Domain/AnimalOwner.cs b/src/DynamicData.Tests/Domain/AnimalOwner.cs
index b960fec87..08925128c 100644
--- a/src/DynamicData.Tests/Domain/AnimalOwner.cs
+++ b/src/DynamicData.Tests/Domain/AnimalOwner.cs
@@ -3,7 +3,7 @@
 
 namespace DynamicData.Tests.Domain;
 
-internal class AnimalOwner(string name, Guid? id = null, bool include = true) : AbstractNotifyPropertyChanged, IDisposable
+internal sealed class AnimalOwner(string name, Guid? id = null, bool include = true) : AbstractNotifyPropertyChanged, IDisposable
 {
     private bool _includeInResults = include;
 
diff --git a/src/DynamicData.Tests/Domain/Market.cs b/src/DynamicData.Tests/Domain/Market.cs
index b7c23b76a..4422df07a 100644
--- a/src/DynamicData.Tests/Domain/Market.cs
+++ b/src/DynamicData.Tests/Domain/Market.cs
@@ -19,7 +19,7 @@ internal interface IMarket
     public IObservable<IChangeSet<MarketPrice, int>> LatestPrices { get; }
 }
 
-internal class Market : IMarket, IDisposable
+internal sealed class Market : IMarket, IDisposable
 {
     private readonly ISourceCache<MarketPrice, int> _latestPrices = new SourceCache<MarketPrice, int>(p => p.ItemId);
 
@@ -108,7 +108,7 @@ public int Compare([DisallowNull] IMarket x, [DisallowNull] IMarket y) =>
 }
 
 
-internal class FixedMarket : IMarket
+internal sealed class FixedMarket : IMarket
 {
     public FixedMarket(Func<decimal> getPrice, int minId, int maxId, bool completable = true)
     {
diff --git a/src/DynamicData.Tests/Domain/MarketPrice.cs b/src/DynamicData.Tests/Domain/MarketPrice.cs
index 05dfaa97b..e88845af5 100644
--- a/src/DynamicData.Tests/Domain/MarketPrice.cs
+++ b/src/DynamicData.Tests/Domain/MarketPrice.cs
@@ -5,7 +5,7 @@
 
 namespace DynamicData.Tests.Domain;
 
-internal class MarketPrice
+internal sealed class MarketPrice
 {
     public static IEqualityComparer<MarketPrice> EqualityComparer { get; } = new CurrentPriceEqualityComparer();
     public static IEqualityComparer<MarketPrice> EqualityComparerWithTimeStamp { get; } = new TimeStampPriceEqualityComparer();
diff --git a/src/DynamicData.Tests/Utilities/ComparerExtensions.cs b/src/DynamicData.Tests/Utilities/ComparerExtensions.cs
index 9bace663b..f14dc74d2 100644
--- a/src/DynamicData.Tests/Utilities/ComparerExtensions.cs
+++ b/src/DynamicData.Tests/Utilities/ComparerExtensions.cs
@@ -4,19 +4,19 @@
 
 namespace DynamicData.Tests.Utilities;
 
-internal class NoOpComparer<T> : IComparer<T>
+internal sealed class NoOpComparer<T> : IComparer<T>
 {
     public int Compare(T x, T y) => throw new NotImplementedException();
 }
 
-internal class NoOpEqualityComparer<T> : IEqualityComparer<T>
+internal sealed class NoOpEqualityComparer<T> : IEqualityComparer<T>
 {
     public bool Equals(T x, T y) => throw new NotImplementedException();
     public int GetHashCode([DisallowNull] T obj) => throw new NotImplementedException();
 }
 
 
-internal class InvertedComparer<T>(IComparer<T> original) : IComparer<T>
+internal sealed class InvertedComparer<T>(IComparer<T> original) : IComparer<T>
 {
     private readonly IComparer<T> _original = original;
 
diff --git a/src/DynamicData/Aggregation/AggregateEnumerator.cs b/src/DynamicData/Aggregation/AggregateEnumerator.cs
index 6cebcf69d..35e18f707 100644
--- a/src/DynamicData/Aggregation/AggregateEnumerator.cs
+++ b/src/DynamicData/Aggregation/AggregateEnumerator.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Aggregation;
 
-internal class AggregateEnumerator<T>(IChangeSet<T> source) : IAggregateChangeSet<T>
+internal sealed class AggregateEnumerator<T>(IChangeSet<T> source) : IAggregateChangeSet<T>
     where T : notnull
 {
     public IEnumerator<AggregateItem<T>> GetEnumerator()
@@ -54,7 +54,7 @@ public IEnumerator<AggregateItem<T>> GetEnumerator()
 }
 
 [SuppressMessage("StyleCop.CSharp.MaintainabilityRules", "SA1402:File may only contain a single type", Justification = "Same name, different generics.")]
-internal class AggregateEnumerator<TObject, TKey>(IChangeSet<TObject, TKey> source) : IAggregateChangeSet<TObject>
+internal sealed class AggregateEnumerator<TObject, TKey>(IChangeSet<TObject, TKey> source) : IAggregateChangeSet<TObject>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Binding/ObservablePropertyFactory.cs b/src/DynamicData/Binding/ObservablePropertyFactory.cs
index 4594fbb59..4def718ed 100644
--- a/src/DynamicData/Binding/ObservablePropertyFactory.cs
+++ b/src/DynamicData/Binding/ObservablePropertyFactory.cs
@@ -9,7 +9,7 @@
 
 namespace DynamicData.Binding;
 
-internal class ObservablePropertyFactory<TObject, TProperty>
+internal sealed class ObservablePropertyFactory<TObject, TProperty>
     where TObject : INotifyPropertyChanged
 {
     private readonly Func<TObject, bool, IObservable<PropertyValue<TObject, TProperty>>> _factory;
diff --git a/src/DynamicData/Cache/DistinctChangeSet.cs b/src/DynamicData/Cache/DistinctChangeSet.cs
index 85df7c997..1717e8788 100644
--- a/src/DynamicData/Cache/DistinctChangeSet.cs
+++ b/src/DynamicData/Cache/DistinctChangeSet.cs
@@ -5,7 +5,7 @@
 // ReSharper disable once CheckNamespace
 namespace DynamicData;
 
-internal class DistinctChangeSet<T> : ChangeSet<T, T>, IDistinctChangeSet<T>
+internal sealed class DistinctChangeSet<T> : ChangeSet<T, T>, IDistinctChangeSet<T>
     where T : notnull
 {
     public DistinctChangeSet(IEnumerable<Change<T, T>> items)
diff --git a/src/DynamicData/Cache/Internal/AutoRefresh.cs b/src/DynamicData/Cache/Internal/AutoRefresh.cs
index 51651ff1e..ecc6e0b72 100644
--- a/src/DynamicData/Cache/Internal/AutoRefresh.cs
+++ b/src/DynamicData/Cache/Internal/AutoRefresh.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class AutoRefresh<TObject, TKey, TAny>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey, IObservable<TAny>> reEvaluator, TimeSpan? buffer = null, IScheduler? scheduler = null)
+internal sealed class AutoRefresh<TObject, TKey, TAny>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey, IObservable<TAny>> reEvaluator, TimeSpan? buffer = null, IScheduler? scheduler = null)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/Cache.cs b/src/DynamicData/Cache/Internal/Cache.cs
index 7a6a62d9b..f4800ad74 100644
--- a/src/DynamicData/Cache/Internal/Cache.cs
+++ b/src/DynamicData/Cache/Internal/Cache.cs
@@ -9,7 +9,7 @@
 namespace DynamicData.Cache.Internal;
 
 [DebuggerDisplay("Cache<{typeof(TObject).Name}, {typeof(TKey).Name}> ({Count} Items)")]
-internal class Cache<TObject, TKey> : ICache<TObject, TKey>
+internal sealed class Cache<TObject, TKey> : ICache<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/CacheUpdater.cs b/src/DynamicData/Cache/Internal/CacheUpdater.cs
index 477cafd50..9f4ab8a84 100644
--- a/src/DynamicData/Cache/Internal/CacheUpdater.cs
+++ b/src/DynamicData/Cache/Internal/CacheUpdater.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class CacheUpdater<TObject, TKey> : ISourceUpdater<TObject, TKey>
+internal sealed class CacheUpdater<TObject, TKey> : ISourceUpdater<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/Cast.cs b/src/DynamicData/Cache/Internal/Cast.cs
index 36f64bd19..296d43562 100644
--- a/src/DynamicData/Cache/Internal/Cast.cs
+++ b/src/DynamicData/Cache/Internal/Cast.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class Cast<TSource, TKey, TDestination>(IObservable<IChangeSet<TSource, TKey>> source, Func<TSource, TDestination> converter)
+internal sealed class Cast<TSource, TKey, TDestination>(IObservable<IChangeSet<TSource, TKey>> source, Func<TSource, TDestination> converter)
     where TSource : notnull
     where TKey : notnull
     where TDestination : notnull
diff --git a/src/DynamicData/Cache/Internal/ChangeSetCache.cs b/src/DynamicData/Cache/Internal/ChangeSetCache.cs
index 4945883eb..d98c0a824 100644
--- a/src/DynamicData/Cache/Internal/ChangeSetCache.cs
+++ b/src/DynamicData/Cache/Internal/ChangeSetCache.cs
@@ -11,7 +11,7 @@ namespace DynamicData.Cache.Internal;
 /// </summary>
 /// <typeparam name="TObject">ChangeSet Object Type.</typeparam>
 /// <typeparam name="TKey">ChangeSet Key Type.</typeparam>
-internal class ChangeSetCache<TObject, TKey>
+internal sealed class ChangeSetCache<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/ChangeSetMergeTracker.cs b/src/DynamicData/Cache/Internal/ChangeSetMergeTracker.cs
index 55464e8e4..ecd2bba98 100644
--- a/src/DynamicData/Cache/Internal/ChangeSetMergeTracker.cs
+++ b/src/DynamicData/Cache/Internal/ChangeSetMergeTracker.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class ChangeSetMergeTracker<TObject, TKey>(Func<IEnumerable<ChangeSetCache<TObject, TKey>>> selectCaches, IComparer<TObject>? comparer, IEqualityComparer<TObject>? equalityComparer)
+internal sealed class ChangeSetMergeTracker<TObject, TKey>(Func<IEnumerable<ChangeSetCache<TObject, TKey>>> selectCaches, IComparer<TObject>? comparer, IEqualityComparer<TObject>? equalityComparer)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/DeferUntilLoaded.cs b/src/DynamicData/Cache/Internal/DeferUntilLoaded.cs
index b28059cd7..e04e2608b 100644
--- a/src/DynamicData/Cache/Internal/DeferUntilLoaded.cs
+++ b/src/DynamicData/Cache/Internal/DeferUntilLoaded.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class DeferUntilLoaded<TObject, TKey>
+internal sealed class DeferUntilLoaded<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/DynamicFilter.cs b/src/DynamicData/Cache/Internal/DynamicFilter.cs
index c75cb7401..2faff65ca 100644
--- a/src/DynamicData/Cache/Internal/DynamicFilter.cs
+++ b/src/DynamicData/Cache/Internal/DynamicFilter.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class DynamicFilter<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, IObservable<Func<TObject, bool>> predicateChanged, IObservable<Unit>? refilterObservable = null, bool suppressEmptyChangeSets = true)
+internal sealed class DynamicFilter<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, IObservable<Func<TObject, bool>> predicateChanged, IObservable<Unit>? refilterObservable = null, bool suppressEmptyChangeSets = true)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/EditDiff.cs b/src/DynamicData/Cache/Internal/EditDiff.cs
index 83ec01b51..ad7271c42 100644
--- a/src/DynamicData/Cache/Internal/EditDiff.cs
+++ b/src/DynamicData/Cache/Internal/EditDiff.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class EditDiff<TObject, TKey>(ISourceCache<TObject, TKey> source, Func<TObject, TObject, bool> areEqual)
+internal sealed class EditDiff<TObject, TKey>(ISourceCache<TObject, TKey> source, Func<TObject, TObject, bool> areEqual)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/FilterOnObservable.cs b/src/DynamicData/Cache/Internal/FilterOnObservable.cs
index 25d334628..9c07397a7 100644
--- a/src/DynamicData/Cache/Internal/FilterOnObservable.cs
+++ b/src/DynamicData/Cache/Internal/FilterOnObservable.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class FilterOnObservable<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey, IObservable<bool>> filterFactory, TimeSpan? buffer = null, IScheduler? scheduler = null)
+internal sealed class FilterOnObservable<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey, IObservable<bool>> filterFactory, TimeSpan? buffer = null, IScheduler? scheduler = null)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/FilterOnProperty.cs b/src/DynamicData/Cache/Internal/FilterOnProperty.cs
index 303cfe8d7..7bb9e7653 100644
--- a/src/DynamicData/Cache/Internal/FilterOnProperty.cs
+++ b/src/DynamicData/Cache/Internal/FilterOnProperty.cs
@@ -9,7 +9,7 @@
 namespace DynamicData.Cache.Internal;
 
 [Obsolete("Use AutoRefresh(), followed by Filter() instead")]
-internal class FilterOnProperty<TObject, TKey, TProperty>(IObservable<IChangeSet<TObject, TKey>> source, Expression<Func<TObject, TProperty>> propertySelector, Func<TObject, bool> predicate, TimeSpan? throttle = null, IScheduler? scheduler = null)
+internal sealed class FilterOnProperty<TObject, TKey, TProperty>(IObservable<IChangeSet<TObject, TKey>> source, Expression<Func<TObject, TProperty>> propertySelector, Func<TObject, bool> predicate, TimeSpan? throttle = null, IScheduler? scheduler = null)
     where TObject : INotifyPropertyChanged
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/FinallySafe.cs b/src/DynamicData/Cache/Internal/FinallySafe.cs
index fb98e1d3c..bb19e6cdf 100644
--- a/src/DynamicData/Cache/Internal/FinallySafe.cs
+++ b/src/DynamicData/Cache/Internal/FinallySafe.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class FinallySafe<T>(IObservable<T> source, Action finallyAction)
+internal sealed class FinallySafe<T>(IObservable<T> source, Action finallyAction)
 {
     private readonly Action _finallyAction = finallyAction ?? throw new ArgumentNullException(nameof(finallyAction));
 
diff --git a/src/DynamicData/Cache/Internal/FullJoin.cs b/src/DynamicData/Cache/Internal/FullJoin.cs
index f2d91f91b..ad75bd62b 100644
--- a/src/DynamicData/Cache/Internal/FullJoin.cs
+++ b/src/DynamicData/Cache/Internal/FullJoin.cs
@@ -9,7 +9,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class FullJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, Optional<TLeft>, Optional<TRight>, TDestination> resultSelector)
+internal sealed class FullJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, Optional<TLeft>, Optional<TRight>, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/FullJoinMany.cs b/src/DynamicData/Cache/Internal/FullJoinMany.cs
index 005f09bc5..77530f4bf 100644
--- a/src/DynamicData/Cache/Internal/FullJoinMany.cs
+++ b/src/DynamicData/Cache/Internal/FullJoinMany.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class FullJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, Optional<TLeft>, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
+internal sealed class FullJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, Optional<TLeft>, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/GroupOnProperty.cs b/src/DynamicData/Cache/Internal/GroupOnProperty.cs
index 094ef7df0..a7353c36c 100644
--- a/src/DynamicData/Cache/Internal/GroupOnProperty.cs
+++ b/src/DynamicData/Cache/Internal/GroupOnProperty.cs
@@ -11,7 +11,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class GroupOnProperty<TObject, TKey, TGroup>(IObservable<IChangeSet<TObject, TKey>> source, Expression<Func<TObject, TGroup>> groupSelectorKey, TimeSpan? throttle = null, IScheduler? scheduler = null)
+internal sealed class GroupOnProperty<TObject, TKey, TGroup>(IObservable<IChangeSet<TObject, TKey>> source, Expression<Func<TObject, TGroup>> groupSelectorKey, TimeSpan? throttle = null, IScheduler? scheduler = null)
     where TObject : INotifyPropertyChanged
     where TKey : notnull
     where TGroup : notnull
diff --git a/src/DynamicData/Cache/Internal/GroupOnPropertyWithImmutableState.cs b/src/DynamicData/Cache/Internal/GroupOnPropertyWithImmutableState.cs
index 515e1d012..7914ebd65 100644
--- a/src/DynamicData/Cache/Internal/GroupOnPropertyWithImmutableState.cs
+++ b/src/DynamicData/Cache/Internal/GroupOnPropertyWithImmutableState.cs
@@ -11,7 +11,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class GroupOnPropertyWithImmutableState<TObject, TKey, TGroup>(IObservable<IChangeSet<TObject, TKey>> source, Expression<Func<TObject, TGroup>> groupSelectorKey, TimeSpan? throttle = null, IScheduler? scheduler = null)
+internal sealed class GroupOnPropertyWithImmutableState<TObject, TKey, TGroup>(IObservable<IChangeSet<TObject, TKey>> source, Expression<Func<TObject, TGroup>> groupSelectorKey, TimeSpan? throttle = null, IScheduler? scheduler = null)
     where TObject : INotifyPropertyChanged
     where TKey : notnull
     where TGroup : notnull
diff --git a/src/DynamicData/Cache/Internal/IndexAndNode.cs b/src/DynamicData/Cache/Internal/IndexAndNode.cs
index 2546b6ece..ca24d3ff3 100644
--- a/src/DynamicData/Cache/Internal/IndexAndNode.cs
+++ b/src/DynamicData/Cache/Internal/IndexAndNode.cs
@@ -12,7 +12,7 @@ internal static class IndexAndNode
 }
 
 [SuppressMessage("StyleCop.CSharp.MaintainabilityRules", "SA1402:File may only contain a single type", Justification = "Same class name, different generics.")]
-internal class IndexAndNode<TNodeValue>(int index, LinkedListNode<TNodeValue> node)
+internal sealed class IndexAndNode<TNodeValue>(int index, LinkedListNode<TNodeValue> node)
 {
     public int Index { get; } = index;
 
diff --git a/src/DynamicData/Cache/Internal/InnerJoin.cs b/src/DynamicData/Cache/Internal/InnerJoin.cs
index 6332aa9c7..c71565ce5 100644
--- a/src/DynamicData/Cache/Internal/InnerJoin.cs
+++ b/src/DynamicData/Cache/Internal/InnerJoin.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class InnerJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<(TLeftKey leftKey, TRightKey rightKey), TLeft, TRight, TDestination> resultSelector)
+internal sealed class InnerJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<(TLeftKey leftKey, TRightKey rightKey), TLeft, TRight, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/InnerJoinMany.cs b/src/DynamicData/Cache/Internal/InnerJoinMany.cs
index 9601a21dd..578e071b8 100644
--- a/src/DynamicData/Cache/Internal/InnerJoinMany.cs
+++ b/src/DynamicData/Cache/Internal/InnerJoinMany.cs
@@ -4,7 +4,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class InnerJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, TLeft, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
+internal sealed class InnerJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, TLeft, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/KeyValueCollection.cs b/src/DynamicData/Cache/Internal/KeyValueCollection.cs
index 5b2d3c641..414e00367 100644
--- a/src/DynamicData/Cache/Internal/KeyValueCollection.cs
+++ b/src/DynamicData/Cache/Internal/KeyValueCollection.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class KeyValueCollection<TObject, TKey> : IKeyValueCollection<TObject, TKey>
+internal sealed class KeyValueCollection<TObject, TKey> : IKeyValueCollection<TObject, TKey>
 {
     private readonly IReadOnlyCollection<KeyValuePair<TKey, TObject>> _items;
 
diff --git a/src/DynamicData/Cache/Internal/KeyValueComparer.cs b/src/DynamicData/Cache/Internal/KeyValueComparer.cs
index fd629e895..c2a4bdcdc 100644
--- a/src/DynamicData/Cache/Internal/KeyValueComparer.cs
+++ b/src/DynamicData/Cache/Internal/KeyValueComparer.cs
@@ -4,7 +4,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class KeyValueComparer<TObject, TKey>(IComparer<TObject>? comparer = null) : IComparer<KeyValuePair<TKey, TObject>>
+internal sealed class KeyValueComparer<TObject, TKey>(IComparer<TObject>? comparer = null) : IComparer<KeyValuePair<TKey, TObject>>
 {
     public int Compare(KeyValuePair<TKey, TObject> x, KeyValuePair<TKey, TObject> y)
     {
diff --git a/src/DynamicData/Cache/Internal/LeftJoin.cs b/src/DynamicData/Cache/Internal/LeftJoin.cs
index ef69cb835..c5a7992d0 100644
--- a/src/DynamicData/Cache/Internal/LeftJoin.cs
+++ b/src/DynamicData/Cache/Internal/LeftJoin.cs
@@ -9,7 +9,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class LeftJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, TLeft, Optional<TRight>, TDestination> resultSelector)
+internal sealed class LeftJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, TLeft, Optional<TRight>, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/LeftJoinMany.cs b/src/DynamicData/Cache/Internal/LeftJoinMany.cs
index fa5921410..dfd1a72c1 100644
--- a/src/DynamicData/Cache/Internal/LeftJoinMany.cs
+++ b/src/DynamicData/Cache/Internal/LeftJoinMany.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class LeftJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, TLeft, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
+internal sealed class LeftJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, TLeft, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/MergeMany.cs b/src/DynamicData/Cache/Internal/MergeMany.cs
index 4fcca76a6..53164855c 100644
--- a/src/DynamicData/Cache/Internal/MergeMany.cs
+++ b/src/DynamicData/Cache/Internal/MergeMany.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class MergeMany<TObject, TKey, TDestination>
+internal sealed class MergeMany<TObject, TKey, TDestination>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/MergeManyItems.cs b/src/DynamicData/Cache/Internal/MergeManyItems.cs
index cbb484355..3282469b7 100644
--- a/src/DynamicData/Cache/Internal/MergeManyItems.cs
+++ b/src/DynamicData/Cache/Internal/MergeManyItems.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class MergeManyItems<TObject, TKey, TDestination>
+internal sealed class MergeManyItems<TObject, TKey, TDestination>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/Page.cs b/src/DynamicData/Cache/Internal/Page.cs
index ed07863d3..a80e597eb 100644
--- a/src/DynamicData/Cache/Internal/Page.cs
+++ b/src/DynamicData/Cache/Internal/Page.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class Page<TObject, TKey>(IObservable<ISortedChangeSet<TObject, TKey>> source, IObservable<IPageRequest> pageRequests)
+internal sealed class Page<TObject, TKey>(IObservable<ISortedChangeSet<TObject, TKey>> source, IObservable<IPageRequest> pageRequests)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/QueryWhenChanged.cs b/src/DynamicData/Cache/Internal/QueryWhenChanged.cs
index c401d1d9d..321bd3ded 100644
--- a/src/DynamicData/Cache/Internal/QueryWhenChanged.cs
+++ b/src/DynamicData/Cache/Internal/QueryWhenChanged.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class QueryWhenChanged<TObject, TKey, TValue>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, IObservable<TValue>>? itemChangedTrigger = null)
+internal sealed class QueryWhenChanged<TObject, TKey, TValue>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, IObservable<TValue>>? itemChangedTrigger = null)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/RefCount.cs b/src/DynamicData/Cache/Internal/RefCount.cs
index 875916095..d9e1fe500 100644
--- a/src/DynamicData/Cache/Internal/RefCount.cs
+++ b/src/DynamicData/Cache/Internal/RefCount.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class RefCount<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source)
+internal sealed class RefCount<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/RemoveKeyEnumerator.cs b/src/DynamicData/Cache/Internal/RemoveKeyEnumerator.cs
index aa29cd4b6..2a7b02e74 100644
--- a/src/DynamicData/Cache/Internal/RemoveKeyEnumerator.cs
+++ b/src/DynamicData/Cache/Internal/RemoveKeyEnumerator.cs
@@ -12,7 +12,7 @@ namespace DynamicData.Cache.Internal;
 /// An optional list, if provided it allows the refresh from a key based cache to find the index for the resulting list based refresh.
 /// If not provided a refresh will dropdown to a replace which may ultimately result in a remove+add change downstream.
 /// </param>
-internal class RemoveKeyEnumerator<TObject, TKey>(IChangeSet<TObject, TKey> source, IExtendedList<TObject>? list = null) : IEnumerable<Change<TObject>>
+internal sealed class RemoveKeyEnumerator<TObject, TKey>(IChangeSet<TObject, TKey> source, IExtendedList<TObject>? list = null) : IEnumerable<Change<TObject>>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/RightJoin.cs b/src/DynamicData/Cache/Internal/RightJoin.cs
index a08552fd8..ca733db25 100644
--- a/src/DynamicData/Cache/Internal/RightJoin.cs
+++ b/src/DynamicData/Cache/Internal/RightJoin.cs
@@ -9,7 +9,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class RightJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TRightKey, Optional<TLeft>, TRight, TDestination> resultSelector)
+internal sealed class RightJoin<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TRightKey, Optional<TLeft>, TRight, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/RightJoinMany.cs b/src/DynamicData/Cache/Internal/RightJoinMany.cs
index cbb7ef519..44879eff5 100644
--- a/src/DynamicData/Cache/Internal/RightJoinMany.cs
+++ b/src/DynamicData/Cache/Internal/RightJoinMany.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class RightJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, Optional<TLeft>, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
+internal sealed class RightJoinMany<TLeft, TLeftKey, TRight, TRightKey, TDestination>(IObservable<IChangeSet<TLeft, TLeftKey>> left, IObservable<IChangeSet<TRight, TRightKey>> right, Func<TRight, TLeftKey> rightKeySelector, Func<TLeftKey, Optional<TLeft>, IGrouping<TRight, TRightKey, TLeftKey>, TDestination> resultSelector)
     where TLeft : notnull
     where TLeftKey : notnull
     where TRight : notnull
diff --git a/src/DynamicData/Cache/Internal/SizeExpirer.cs b/src/DynamicData/Cache/Internal/SizeExpirer.cs
index d719453b2..3e4155c58 100644
--- a/src/DynamicData/Cache/Internal/SizeExpirer.cs
+++ b/src/DynamicData/Cache/Internal/SizeExpirer.cs
@@ -9,7 +9,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class SizeExpirer<TObject, TKey>
+internal sealed class SizeExpirer<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/SpecifiedGrouper.cs b/src/DynamicData/Cache/Internal/SpecifiedGrouper.cs
index ba6bd9753..292e0112d 100644
--- a/src/DynamicData/Cache/Internal/SpecifiedGrouper.cs
+++ b/src/DynamicData/Cache/Internal/SpecifiedGrouper.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class SpecifiedGrouper<TObject, TKey, TGroupKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TGroupKey> groupSelector, IObservable<IDistinctChangeSet<TGroupKey>> resultGroupSource)
+internal sealed class SpecifiedGrouper<TObject, TKey, TGroupKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TGroupKey> groupSelector, IObservable<IDistinctChangeSet<TGroupKey>> resultGroupSource)
     where TObject : notnull
     where TKey : notnull
     where TGroupKey : notnull
diff --git a/src/DynamicData/Cache/Internal/StaticFilter.cs b/src/DynamicData/Cache/Internal/StaticFilter.cs
index 35c451ee0..d6fc7cbe5 100644
--- a/src/DynamicData/Cache/Internal/StaticFilter.cs
+++ b/src/DynamicData/Cache/Internal/StaticFilter.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class StaticFilter<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, bool> filter, bool suppressEmptyChangeSets)
+internal sealed class StaticFilter<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, bool> filter, bool suppressEmptyChangeSets)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/StatusMonitor.cs b/src/DynamicData/Cache/Internal/StatusMonitor.cs
index ff9bb23e7..8aad491f1 100644
--- a/src/DynamicData/Cache/Internal/StatusMonitor.cs
+++ b/src/DynamicData/Cache/Internal/StatusMonitor.cs
@@ -10,7 +10,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class StatusMonitor<T>(IObservable<T> source)
+internal sealed class StatusMonitor<T>(IObservable<T> source)
 {
     public IObservable<ConnectionStatus> Run() => Observable.Create<ConnectionStatus>(
             observer =>
diff --git a/src/DynamicData/Cache/Internal/SubscribeMany.cs b/src/DynamicData/Cache/Internal/SubscribeMany.cs
index a61a68610..bf6eb1d9f 100644
--- a/src/DynamicData/Cache/Internal/SubscribeMany.cs
+++ b/src/DynamicData/Cache/Internal/SubscribeMany.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class SubscribeMany<TObject, TKey>
+internal sealed class SubscribeMany<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/TimeExpirer.cs b/src/DynamicData/Cache/Internal/TimeExpirer.cs
index 991638434..ad48c800b 100644
--- a/src/DynamicData/Cache/Internal/TimeExpirer.cs
+++ b/src/DynamicData/Cache/Internal/TimeExpirer.cs
@@ -10,7 +10,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class TimeExpirer<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TimeSpan?> timeSelector, TimeSpan? interval, IScheduler scheduler)
+internal sealed class TimeExpirer<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TimeSpan?> timeSelector, TimeSpan? interval, IScheduler scheduler)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/ToObservableChangeSet.cs b/src/DynamicData/Cache/Internal/ToObservableChangeSet.cs
index 842331bcb..7b1656074 100644
--- a/src/DynamicData/Cache/Internal/ToObservableChangeSet.cs
+++ b/src/DynamicData/Cache/Internal/ToObservableChangeSet.cs
@@ -9,7 +9,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class ToObservableChangeSet<TObject, TKey>
+internal sealed class ToObservableChangeSet<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/ToObservableOptional.cs b/src/DynamicData/Cache/Internal/ToObservableOptional.cs
index e849a5158..15e8f8684 100644
--- a/src/DynamicData/Cache/Internal/ToObservableOptional.cs
+++ b/src/DynamicData/Cache/Internal/ToObservableOptional.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class ToObservableOptional<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, TKey key, IEqualityComparer<TObject>? equalityComparer = null)
+internal sealed class ToObservableOptional<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, TKey key, IEqualityComparer<TObject>? equalityComparer = null)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/TransformAsync.cs b/src/DynamicData/Cache/Internal/TransformAsync.cs
index 6f0d69c2b..2b0b5788a 100644
--- a/src/DynamicData/Cache/Internal/TransformAsync.cs
+++ b/src/DynamicData/Cache/Internal/TransformAsync.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class TransformAsync<TDestination, TSource, TKey>(IObservable<IChangeSet<TSource, TKey>> source, Func<TSource, Optional<TSource>, TKey, Task<TDestination>> transformFactory, Action<Error<TSource, TKey>>? exceptionCallback, IObservable<Func<TSource, TKey, bool>>? forceTransform = null)
+internal sealed class TransformAsync<TDestination, TSource, TKey>(IObservable<IChangeSet<TSource, TKey>> source, Func<TSource, Optional<TSource>, TKey, Task<TDestination>> transformFactory, Action<Error<TSource, TKey>>? exceptionCallback, IObservable<Func<TSource, TKey, bool>>? forceTransform = null)
     where TDestination : notnull
     where TSource : notnull
     where TKey : notnull
diff --git a/src/DynamicData/Cache/Internal/TransformMany.cs b/src/DynamicData/Cache/Internal/TransformMany.cs
index bd5d8efb8..f8fe8d2b3 100644
--- a/src/DynamicData/Cache/Internal/TransformMany.cs
+++ b/src/DynamicData/Cache/Internal/TransformMany.cs
@@ -12,7 +12,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class TransformMany<TDestination, TDestinationKey, TSource, TSourceKey>(IObservable<IChangeSet<TSource, TSourceKey>> source, Func<TSource, IEnumerable<TDestination>> manySelector, Func<TDestination, TDestinationKey> keySelector, Func<TSource, IObservable<IChangeSet<TDestination, TDestinationKey>>>? childChanges = null)
+internal sealed class TransformMany<TDestination, TDestinationKey, TSource, TSourceKey>(IObservable<IChangeSet<TSource, TSourceKey>> source, Func<TSource, IEnumerable<TDestination>> manySelector, Func<TDestination, TDestinationKey> keySelector, Func<TSource, IObservable<IChangeSet<TDestination, TDestinationKey>>>? childChanges = null)
     where TDestination : notnull
     where TDestinationKey : notnull
     where TSource : notnull
diff --git a/src/DynamicData/Cache/Internal/TreeBuilder.cs b/src/DynamicData/Cache/Internal/TreeBuilder.cs
index 72f903e41..6f679b9f4 100644
--- a/src/DynamicData/Cache/Internal/TreeBuilder.cs
+++ b/src/DynamicData/Cache/Internal/TreeBuilder.cs
@@ -11,7 +11,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class TreeBuilder<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey> pivotOn, IObservable<Func<Node<TObject, TKey>, bool>>? predicateChanged)
+internal sealed class TreeBuilder<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey> pivotOn, IObservable<Func<Node<TObject, TKey>, bool>>? predicateChanged)
     where TObject : class
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/Internal/TrueFor.cs b/src/DynamicData/Cache/Internal/TrueFor.cs
index 5c7c7b54a..333cc69d1 100644
--- a/src/DynamicData/Cache/Internal/TrueFor.cs
+++ b/src/DynamicData/Cache/Internal/TrueFor.cs
@@ -7,7 +7,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class TrueFor<TObject, TKey, TValue>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, IObservable<TValue>> observableSelector, Func<IEnumerable<ObservableWithValue<TObject, TValue>>, bool> collectionMatcher)
+internal sealed class TrueFor<TObject, TKey, TValue>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, IObservable<TValue>> observableSelector, Func<IEnumerable<ObservableWithValue<TObject, TValue>>, bool> collectionMatcher)
     where TObject : notnull
     where TKey : notnull
     where TValue : notnull
diff --git a/src/DynamicData/Cache/Internal/UniquenessEnforcer.cs b/src/DynamicData/Cache/Internal/UniquenessEnforcer.cs
index e86c2d1a1..53bf65ac5 100644
--- a/src/DynamicData/Cache/Internal/UniquenessEnforcer.cs
+++ b/src/DynamicData/Cache/Internal/UniquenessEnforcer.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.Cache.Internal;
 
-internal class UniquenessEnforcer<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source)
+internal sealed class UniquenessEnforcer<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source)
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Cache/SortedChangeSet.cs b/src/DynamicData/Cache/SortedChangeSet.cs
index e39079e77..0a1bf615e 100644
--- a/src/DynamicData/Cache/SortedChangeSet.cs
+++ b/src/DynamicData/Cache/SortedChangeSet.cs
@@ -7,7 +7,7 @@
 // ReSharper disable once CheckNamespace
 namespace DynamicData;
 
-internal class SortedChangeSet<TObject, TKey> : ChangeSet<TObject, TKey>, ISortedChangeSet<TObject, TKey>
+internal sealed class SortedChangeSet<TObject, TKey> : ChangeSet<TObject, TKey>, ISortedChangeSet<TObject, TKey>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/Experimental/SubjectWithRefCount.cs b/src/DynamicData/Experimental/SubjectWithRefCount.cs
index 38903dc33..55d359080 100644
--- a/src/DynamicData/Experimental/SubjectWithRefCount.cs
+++ b/src/DynamicData/Experimental/SubjectWithRefCount.cs
@@ -15,7 +15,7 @@ namespace DynamicData.Experimental;
 /// Initializes a new instance of the <see cref="SubjectWithRefCount{T}"/> class.
 /// </remarks>
 /// <param name="subject">The subject to perform reference counting on.</param>
-internal class SubjectWithRefCount<T>(ISubject<T>? subject = null) : ISubjectWithRefCount<T>
+internal sealed class SubjectWithRefCount<T>(ISubject<T>? subject = null) : ISubjectWithRefCount<T>
 {
     private readonly ISubject<T> _subject = subject ?? new Subject<T>();
 
diff --git a/src/DynamicData/Kernel/ReferenceEqualityComparer.cs b/src/DynamicData/Kernel/ReferenceEqualityComparer.cs
index 2af0b2e6c..e1e6ae703 100644
--- a/src/DynamicData/Kernel/ReferenceEqualityComparer.cs
+++ b/src/DynamicData/Kernel/ReferenceEqualityComparer.cs
@@ -4,7 +4,7 @@
 
 namespace DynamicData.Kernel;
 
-internal class ReferenceEqualityComparer<T> : IEqualityComparer<T>
+internal sealed class ReferenceEqualityComparer<T> : IEqualityComparer<T>
 {
     public static readonly IEqualityComparer<T> Instance = new ReferenceEqualityComparer<T>();
 
diff --git a/src/DynamicData/List/ChangeAwareListWithRefCounts.cs b/src/DynamicData/List/ChangeAwareListWithRefCounts.cs
index eaf237894..2467bc952 100644
--- a/src/DynamicData/List/ChangeAwareListWithRefCounts.cs
+++ b/src/DynamicData/List/ChangeAwareListWithRefCounts.cs
@@ -8,7 +8,7 @@
 // ReSharper disable once CheckNamespace
 namespace DynamicData;
 
-internal class ChangeAwareListWithRefCounts<T> : ChangeAwareList<T>
+internal sealed class ChangeAwareListWithRefCounts<T> : ChangeAwareList<T>
     where T : notnull
 {
     private readonly ReferenceCountTracker<T> _tracker = new();
diff --git a/src/DynamicData/List/Linq/AddKeyEnumerator.cs b/src/DynamicData/List/Linq/AddKeyEnumerator.cs
index d51883eba..ef288a1c7 100644
--- a/src/DynamicData/List/Linq/AddKeyEnumerator.cs
+++ b/src/DynamicData/List/Linq/AddKeyEnumerator.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.List.Linq;
 
-internal class AddKeyEnumerator<TObject, TKey>(IChangeSet<TObject> source, Func<TObject, TKey> keySelector) : IEnumerable<Change<TObject, TKey>>
+internal sealed class AddKeyEnumerator<TObject, TKey>(IChangeSet<TObject> source, Func<TObject, TKey> keySelector) : IEnumerable<Change<TObject, TKey>>
     where TObject : notnull
     where TKey : notnull
 {
diff --git a/src/DynamicData/List/Linq/ItemChangeEnumerator.cs b/src/DynamicData/List/Linq/ItemChangeEnumerator.cs
index f575c24bc..9736149dc 100644
--- a/src/DynamicData/List/Linq/ItemChangeEnumerator.cs
+++ b/src/DynamicData/List/Linq/ItemChangeEnumerator.cs
@@ -6,7 +6,7 @@
 
 namespace DynamicData.List.Linq;
 
-internal class ItemChangeEnumerator<T>(IChangeSet<T> changeSet) : IEnumerable<ItemChange<T>>
+internal sealed class ItemChangeEnumerator<T>(IChangeSet<T> changeSet) : IEnumerable<ItemChange<T>>
     where T : notnull
 {
     public IEnumerator<ItemChange<T>> GetEnumerator()
diff --git a/src/DynamicData/List/Linq/Reverser.cs b/src/DynamicData/List/Linq/Reverser.cs
index 9e91ba5a5..67cf918d1 100644
--- a/src/DynamicData/List/Linq/Reverser.cs
+++ b/src/DynamicData/List/Linq/Reverser.cs
@@ -4,7 +4,7 @@
 
 namespace DynamicData.List.Linq;
 
-internal class Reverser<T>
+internal sealed class Reverser<T>
     where T : notnull
 {
     private int _length;
diff --git a/src/DynamicData/List/Linq/UnifiedChangeEnumerator.cs b/src/DynamicData/List/Linq/UnifiedChangeEnumerator.cs
index 3f511f484..2c81f8da2 100644
--- a/src/DynamicData/List/Linq/UnifiedChangeEnumerator.cs
+++ b/src/DynamicData/List/Linq/UnifiedChangeEnumerator.cs
@@ -8,7 +8,7 @@
 
 namespace DynamicData.List.Linq;
 
-internal class UnifiedChangeEnumerator<T>(IChangeSet<T> changeSet) : IEnumerable<UnifiedChange<T>>
+internal sealed class UnifiedChangeEnumerator<T>(IChangeSet<T> changeSet) : IEnumerable<UnifiedChange<T>>
     where T : notnull
 {
     public IEnumerator<UnifiedChange<T>> GetEnumerator()
diff --git a/src/DynamicData/List/Linq/WithoutIndexEnumerator.cs b/src/DynamicData/List/Linq/WithoutIndexEnumerator.cs
index 31d7505e0..47f02f031 100644
--- a/src/DynamicData/List/Linq/WithoutIndexEnumerator.cs
+++ b/src/DynamicData/List/Linq/WithoutIndexEnumerator.cs
@@ -11,7 +11,7 @@ namespace DynamicData.List.Linq;
 /// Otherwise these operators could break subsequent operators when the subsequent operator relies on the index.
 /// </summary>
 /// <typeparam name="T">The type of the item.</typeparam>
-internal class WithoutIndexEnumerator<T>(IEnumerable<Change<T>> changeSet) : IEnumerable<Change<T>>
+internal sealed class WithoutIndexEnumerator<T>(IEnumerable<Change<T>> changeSet) : IEnumerable<Change<T>>
     where T : notnull
 {
     public IEnumerator<Change<T>> GetEnumerator()
diff --git a/src/DynamicData/List/VirtualChangeSet.cs b/src/DynamicData/List/VirtualChangeSet.cs
index f5b733895..bf62b059e 100644
--- a/src/DynamicData/List/VirtualChangeSet.cs
+++ b/src/DynamicData/List/VirtualChangeSet.cs
@@ -7,7 +7,7 @@
 // ReSharper disable once CheckNamespace
 namespace DynamicData;
 
-internal class VirtualChangeSet<T>(IChangeSet<T> virtualChangeSet, IVirtualResponse response) : IVirtualChangeSet<T>
+internal sealed class VirtualChangeSet<T>(IChangeSet<T> virtualChangeSet, IVirtualResponse response) : IVirtualChangeSet<T>
     where T : notnull
 {
     private readonly IChangeSet<T> _virtualChangeSet = virtualChangeSet ?? throw new ArgumentNullException(nameof(virtualChangeSet));
diff --git a/src/DynamicData/Platforms/net45/PFilter.cs b/src/DynamicData/Platforms/net45/PFilter.cs
index 8a04b791d..97887fe88 100644
--- a/src/DynamicData/Platforms/net45/PFilter.cs
+++ b/src/DynamicData/Platforms/net45/PFilter.cs
@@ -11,7 +11,7 @@
 // ReSharper disable once CheckNamespace
 namespace DynamicData.PLinq
 {
-    internal class PFilter<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, bool> filter, ParallelisationOptions parallelisationOptions)
+    internal sealed class PFilter<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, bool> filter, ParallelisationOptions parallelisationOptions)
         where TObject : notnull
         where TKey : notnull
     {
diff --git a/src/DynamicData/Platforms/net45/PSubscribeMany.cs b/src/DynamicData/Platforms/net45/PSubscribeMany.cs
index 294cdce15..1ab71c2c8 100644
--- a/src/DynamicData/Platforms/net45/PSubscribeMany.cs
+++ b/src/DynamicData/Platforms/net45/PSubscribeMany.cs
@@ -9,7 +9,7 @@
 // ReSharper disable once CheckNamespace
 namespace DynamicData.PLinq
 {
-    internal class PSubscribeMany<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey, IDisposable> subscriptionFactory, ParallelisationOptions parallelisationOptions)
+    internal sealed class PSubscribeMany<TObject, TKey>(IObservable<IChangeSet<TObject, TKey>> source, Func<TObject, TKey, IDisposable> subscriptionFactory, ParallelisationOptions parallelisationOptions)
         where TObject : notnull
         where TKey : notnull
     {