diff --git a/src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelList.cs b/src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelList.cs
index a6e5e3a3fe975..bd3a854f39a64 100644
--- a/src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelList.cs
+++ b/src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelList.cs
@@ -31,7 +31,6 @@ namespace System.Collections.Generic
     // LowLevelList with no interface implementation minimizes both code and data size.
     // Data size is smaller because there will be minimal virtual function table.
     // Code size is smaller because only functions called will be in the binary.
-    // Use LowLevelListWithIList<T> for IList support
     [DebuggerDisplay("Count = {Count}")]
 #if TYPE_LOADER_IMPLEMENTATION
     [System.Runtime.CompilerServices.ForceDictionaryLookups]
@@ -196,356 +195,5 @@ private void EnsureCapacity(int min)
                 Capacity = newCapacity;
             }
         }
-
-#if !TYPE_LOADER_IMPLEMENTATION
-        // Adds the elements of the given collection to the end of this list. If
-        // required, the capacity of the list is increased to twice the previous
-        // capacity or the new size, whichever is larger.
-        //
-        public void AddRange(IEnumerable<T> collection)
-        {
-
-            InsertRange(_size, collection);
-        }
-
-        // Clears the contents of List.
-        public void Clear()
-        {
-            if (_size > 0)
-            {
-                Array.Clear(_items, 0, _size); // Don't need to doc this but we clear the elements so that the gc can reclaim the references.
-                _size = 0;
-            }
-            _version++;
-        }
-
-        // Contains returns true if the specified element is in the List.
-        // It does a linear, O(n) search.  Equality is determined by calling
-        // item.Equals().
-        //
-        public bool Contains(T item)
-        {
-            if ((object?)item == null)
-            {
-                for (int i = 0; i < _size; i++)
-                    if ((object?)_items[i] == null)
-                        return true;
-                return false;
-            }
-            else
-            {
-                int index = IndexOf(item);
-                if (index >= 0)
-                    return true;
-                return false;
-            }
-        }
-
-
-        // Copies a section of this list to the given array at the given index.
-        //
-        // The method uses the Array.Copy method to copy the elements.
-        //
-        public void CopyTo(int index, T[] array, int arrayIndex, int count)
-        {
-            if (_size - index < count)
-            {
-                throw new ArgumentException();
-            }
-
-            // Delegate rest of error checking to Array.Copy.
-            Array.Copy(_items, index, array, arrayIndex, count);
-        }
-
-        public void CopyTo(T[] array, int arrayIndex)
-        {
-            // Delegate rest of error checking to Array.Copy.
-            Array.Copy(_items, 0, array, arrayIndex, _size);
-        }
-
-        // Returns the index of the first occurrence of a given value in a range of
-        // this list. The list is searched forwards from beginning to end.
-        // The elements of the list are compared to the given value using the
-        // Object.Equals method.
-        //
-        // This method uses the Array.IndexOf method to perform the
-        // search.
-        //
-        public int IndexOf(T item)
-        {
-            return Array.IndexOf(_items, item, 0, _size);
-        }
-
-
-        // Returns the index of the first occurrence of a given value in a range of
-        // this list. The list is searched forwards, starting at index
-        // index and ending at count number of elements. The
-        // elements of the list are compared to the given value using the
-        // Object.Equals method.
-        //
-        // This method uses the Array.IndexOf method to perform the
-        // search.
-        //
-        public int IndexOf(T item, int index)
-        {
-            ArgumentOutOfRangeException.ThrowIfGreaterThan(index, _size);
-            return Array.IndexOf(_items, item, index, _size - index);
-        }
-
-        // Inserts an element into this list at a given index. The size of the list
-        // is increased by one. If required, the capacity of the list is doubled
-        // before inserting the new element.
-        //
-        public void Insert(int index, T item)
-        {
-            // Note that insertions at the end are legal.
-            ArgumentOutOfRangeException.ThrowIfGreaterThan((uint)index, (uint)_size, nameof(index));
-
-            if (_size == _items.Length) EnsureCapacity(_size + 1);
-            if (index < _size)
-            {
-                Array.Copy(_items, index, _items, index + 1, _size - index);
-            }
-            _items[index] = item;
-            _size++;
-            _version++;
-        }
-
-        // Inserts the elements of the given collection at a given index. If
-        // required, the capacity of the list is increased to twice the previous
-        // capacity or the new size, whichever is larger.  Ranges may be added
-        // to the end of the list by setting index to the List's size.
-        //
-        public void InsertRange(int index, IEnumerable<T> collection)
-        {
-            ArgumentNullException.ThrowIfNull(collection);
-            ArgumentOutOfRangeException.ThrowIfGreaterThan((uint)index, (uint)_size, nameof(index));
-
-            ICollection<T>? c = collection as ICollection<T>;
-            if (c != null)
-            {    // if collection is ICollection<T>
-                int count = c.Count;
-                if (count > 0)
-                {
-                    EnsureCapacity(_size + count);
-                    if (index < _size)
-                    {
-                        Array.Copy(_items, index, _items, index + count, _size - index);
-                    }
-
-                    // If we're inserting a List into itself, we want to be able to deal with that.
-                    if (this == c)
-                    {
-                        // Copy first part of _items to insert location
-                        Array.Copy(_items, 0, _items, index, index);
-                        // Copy last part of _items back to inserted location
-                        Array.Copy(_items, index + count, _items, index * 2, _size - index);
-                    }
-                    else
-                    {
-                        T[] itemsToInsert = new T[count];
-                        c.CopyTo(itemsToInsert, 0);
-                        Array.Copy(itemsToInsert, 0, _items, index, count);
-                    }
-                    _size += count;
-                }
-            }
-            else
-            {
-                using (IEnumerator<T> en = collection.GetEnumerator())
-                {
-                    while (en.MoveNext())
-                    {
-                        Insert(index++, en.Current);
-                    }
-                }
-            }
-            _version++;
-        }
-
-        // Removes the element at the given index. The size of the list is
-        // decreased by one.
-        //
-        public bool Remove(T item)
-        {
-            int index = IndexOf(item);
-            if (index >= 0)
-            {
-                RemoveAt(index);
-                return true;
-            }
-
-            return false;
-        }
-
-        // This method removes all items which matches the predicate.
-        // The complexity is O(n).
-        public int RemoveAll(Predicate<T> match)
-        {
-            ArgumentNullException.ThrowIfNull(match);
-
-            int freeIndex = 0;   // the first free slot in items array
-
-            // Find the first item which needs to be removed.
-            while (freeIndex < _size && !match(_items[freeIndex]!)) freeIndex++;
-            if (freeIndex >= _size) return 0;
-
-            int current = freeIndex + 1;
-            while (current < _size)
-            {
-                // Find the first item which needs to be kept.
-                while (current < _size && match(_items[current]!)) current++;
-
-                if (current < _size)
-                {
-                    // copy item to the free slot.
-                    _items[freeIndex++] = _items[current++];
-                }
-            }
-
-            Array.Clear(_items, freeIndex, _size - freeIndex);
-            int result = _size - freeIndex;
-            _size = freeIndex;
-            _version++;
-            return result;
-        }
-
-        // Removes the element at the given index. The size of the list is
-        // decreased by one.
-        //
-        public void RemoveAt(int index)
-        {
-            ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual((uint)index, (uint)_size, nameof(index));
-            _size--;
-            if (index < _size)
-            {
-                Array.Copy(_items, index + 1, _items, index, _size - index);
-            }
-            _items[_size] = default!;
-            _version++;
-        }
-
-        // ToArray returns a new Object array containing the contents of the List.
-        // This requires copying the List, which is an O(n) operation.
-        public T[] ToArray()
-        {
-            T[] array = new T[_size];
-            Array.Copy(_items, 0, array, 0, _size);
-            return array;
-        }
-#endif
-    }
-
-#if !TYPE_LOADER_IMPLEMENTATION
-    // LowLevelList<T> with full IList<T> implementation
-    internal sealed class LowLevelListWithIList<T> : LowLevelList<T>, IList<T>
-    {
-        public LowLevelListWithIList()
-        {
-        }
-
-        public LowLevelListWithIList(int capacity)
-            : base(capacity)
-        {
-        }
-
-        public LowLevelListWithIList(IEnumerable<T> collection)
-            : base(collection)
-        {
-        }
-
-        // Is this List read-only?
-        bool ICollection<T>.IsReadOnly
-        {
-            get { return false; }
-        }
-
-        /// <internalonly/>
-        IEnumerator<T> IEnumerable<T>.GetEnumerator()
-        {
-            return new Enumerator(this);
-        }
-
-        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
-        {
-            return new Enumerator(this);
-        }
-
-        private struct Enumerator : IEnumerator<T>, System.Collections.IEnumerator
-        {
-            private LowLevelListWithIList<T> _list;
-            private int _index;
-            private int _version;
-            private T? _current;
-
-            internal Enumerator(LowLevelListWithIList<T> list)
-            {
-                _list = list;
-                _index = 0;
-                _version = list._version;
-                _current = default(T);
-            }
-
-            public void Dispose()
-            {
-            }
-
-            public bool MoveNext()
-            {
-                LowLevelListWithIList<T> localList = _list;
-
-                if (_version == localList._version && ((uint)_index < (uint)localList._size))
-                {
-                    _current = localList._items[_index];
-                    _index++;
-                    return true;
-                }
-                return MoveNextRare();
-            }
-
-            private bool MoveNextRare()
-            {
-                if (_version != _list._version)
-                {
-                    throw new InvalidOperationException();
-                }
-
-                _index = _list._size + 1;
-                _current = default(T);
-                return false;
-            }
-
-            public T Current
-            {
-                get
-                {
-                    return _current!;
-                }
-            }
-
-            object? System.Collections.IEnumerator.Current
-            {
-                get
-                {
-                    if (_index == 0 || _index == _list._size + 1)
-                    {
-                        throw new InvalidOperationException();
-                    }
-                    return Current;
-                }
-            }
-
-            void System.Collections.IEnumerator.Reset()
-            {
-                if (_version != _list._version)
-                {
-                    throw new InvalidOperationException();
-                }
-
-                _index = 0;
-                _current = default(T);
-            }
-        }
     }
-#endif // !TYPE_LOADER_IMPLEMENTATION
 }
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Attribute.NativeAot.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Attribute.NativeAot.cs
index a619095037b5c..b68c2234d88fa 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Attribute.NativeAot.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Attribute.NativeAot.cs
@@ -135,18 +135,23 @@ private static Attribute OneOrNull(IEnumerable<CustomAttributeData> results)
             Justification = "Arrays of reference types are safe to create.")]
         private static Attribute[] Instantiate(IEnumerable<CustomAttributeData> cads, Type actualElementType)
         {
-            LowLevelList<Attribute> attributes = new LowLevelList<Attribute>();
+            ArrayBuilder<Attribute> attributes = default;
             foreach (CustomAttributeData cad in cads)
             {
                 Attribute instantiatedAttribute = cad.Instantiate();
                 attributes.Add(instantiatedAttribute);
             }
-            int count = attributes.Count;
-            Attribute[] result = actualElementType.ContainsGenericParameters
-                ? new Attribute[count]
-                : (Attribute[])Array.CreateInstance(actualElementType, count);
-            attributes.CopyTo(result, 0);
-            return result;
+
+            if (actualElementType.ContainsGenericParameters)
+            {
+                return attributes.ToArray();
+            }
+            else
+            {
+                Attribute[] result = (Attribute[])Array.CreateInstance(actualElementType, attributes.Count);
+                attributes.CopyTo(result);
+                return result;
+            }
         }
     }
 }
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/NativeFormat/NativeFormatCustomAttributeData.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/NativeFormat/NativeFormatCustomAttributeData.cs
index 10c49ffe177bb..e7a7202b0400c 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/NativeFormat/NativeFormatCustomAttributeData.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/NativeFormat/NativeFormatCustomAttributeData.cs
@@ -116,7 +116,7 @@ internal sealed override IList<CustomAttributeTypedArgument> GetConstructorArgum
             }
             Handle[] ctorTypeHandles = parameterTypeSignatureHandles.ToArray();
 
-            LowLevelListWithIList<CustomAttributeTypedArgument> customAttributeTypedArguments = new LowLevelListWithIList<CustomAttributeTypedArgument>();
+            ArrayBuilder<CustomAttributeTypedArgument> customAttributeTypedArguments = new ArrayBuilder<CustomAttributeTypedArgument>(_customAttribute.FixedArguments.Count);
             foreach (Handle fixedArgumentHandle in _customAttribute.FixedArguments)
             {
                 Handle typeHandle = ctorTypeHandles[index];
@@ -147,7 +147,7 @@ internal sealed override IList<CustomAttributeTypedArgument> GetConstructorArgum
                 index++;
             }
 
-            return customAttributeTypedArguments;
+            return customAttributeTypedArguments.ToArray();
         }
 
         //
@@ -155,7 +155,7 @@ internal sealed override IList<CustomAttributeTypedArgument> GetConstructorArgum
         //
         internal sealed override IList<CustomAttributeNamedArgument> GetNamedArguments(bool throwIfMissingMetadata)
         {
-            LowLevelListWithIList<CustomAttributeNamedArgument> customAttributeNamedArguments = new LowLevelListWithIList<CustomAttributeNamedArgument>();
+            ArrayBuilder<CustomAttributeNamedArgument> customAttributeNamedArguments = new ArrayBuilder<CustomAttributeNamedArgument>(_customAttribute.NamedArguments.Count);
             foreach (NamedArgumentHandle namedArgumentHandle in _customAttribute.NamedArguments)
             {
                 NamedArgument namedArgument = namedArgumentHandle.GetNamedArgument(_reader);
@@ -185,7 +185,7 @@ internal sealed override IList<CustomAttributeNamedArgument> GetNamedArguments(b
 
                 customAttributeNamedArguments.Add(CreateCustomAttributeNamedArgument(this.AttributeType, memberName, isField, typedValue));
             }
-            return customAttributeNamedArguments;
+            return customAttributeNamedArguments.ToArray();
         }
 
         [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2070:UnrecognizedReflectionPattern",
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/RuntimeCustomAttributeData.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/RuntimeCustomAttributeData.cs
index 12b0cde3b166f..12b6000851694 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/RuntimeCustomAttributeData.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/CustomAttributes/RuntimeCustomAttributeData.cs
@@ -171,13 +171,13 @@ protected static CustomAttributeTypedArgument WrapInCustomAttributeTypedArgument
                 if (!argumentType.IsArray)
                     throw new BadImageFormatException();
                 Type reportedElementType = argumentType.GetElementType()!;
-                LowLevelListWithIList<CustomAttributeTypedArgument> elementTypedArguments = new LowLevelListWithIList<CustomAttributeTypedArgument>();
+                ArrayBuilder<CustomAttributeTypedArgument> elementTypedArguments = default;
                 foreach (object elementValue in enumerableValue)
                 {
                     CustomAttributeTypedArgument elementTypedArgument = WrapInCustomAttributeTypedArgument(elementValue, reportedElementType);
                     elementTypedArguments.Add(elementTypedArgument);
                 }
-                return new CustomAttributeTypedArgument(argumentType, new ReadOnlyCollection<CustomAttributeTypedArgument>(elementTypedArguments));
+                return new CustomAttributeTypedArgument(argumentType, new ReadOnlyCollection<CustomAttributeTypedArgument>(elementTypedArguments.ToArray()));
             }
             else
             {
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/Helpers.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/Helpers.cs
index abe62427fb1dd..b6d019046c388 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/Helpers.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/Helpers.cs
@@ -151,22 +151,26 @@ public static BinderBundle ToBinderBundle(this Binder binder, BindingFlags invok
             Justification = "Array.CreateInstance is only used with reference types here and is therefore safe.")]
         public static object[] InstantiateAsArray(this IEnumerable<CustomAttributeData> cads, Type actualElementType)
         {
-            LowLevelList<object> attributes = new LowLevelList<object>();
+            ArrayBuilder<object> attributes = default;
             foreach (CustomAttributeData cad in cads)
             {
                 object instantiatedAttribute = cad.Instantiate();
                 attributes.Add(instantiatedAttribute);
             }
 
-            // This is here for desktop compatibility. ICustomAttribute.GetCustomAttributes() normally returns an array of the
-            // exact attribute type requested except in two cases: when the passed in type is an open type and when
-            // it is a value type. In these two cases, it returns an array of type Object[].
-            bool useObjectArray = actualElementType.ContainsGenericParameters || actualElementType.IsValueType;
-            int count = attributes.Count;
-            object[] result = useObjectArray ? new object[count] : (object[])Array.CreateInstance(actualElementType, count);
-
-            attributes.CopyTo(result, 0);
-            return result;
+            if (actualElementType.ContainsGenericParameters || actualElementType.IsValueType)
+            {
+                // This is here for desktop compatibility. ICustomAttribute.GetCustomAttributes() normally returns an array of the
+                // exact attribute type requested except in two cases: when the passed in type is an open type and when
+                // it is a value type. In these two cases, it returns an array of type Object[].
+                return attributes.ToArray();
+            }
+            else
+            {
+                object[] result = (object[])Array.CreateInstance(actualElementType, attributes.Count);
+                attributes.CopyTo(result);
+                return result;
+            }
         }
 
         private static object? GetRawDefaultValue(IEnumerable<CustomAttributeData> customAttributes)
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/MetadataReaderExtensions.NativeFormat.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/MetadataReaderExtensions.NativeFormat.cs
index f9f89d7343575..46ad09d02bf66 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/MetadataReaderExtensions.NativeFormat.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/MetadataReaderExtensions.NativeFormat.cs
@@ -79,20 +79,21 @@ internal static Type[] GetCustomModifiers(this Handle handle, MetadataReader rea
             if (handleType != HandleType.ModifiedType)
                 return Array.Empty<Type>();
 
-            LowLevelList<Type> customModifiers = new LowLevelList<Type>();
+            ArrayBuilder<Type> customModifiers = default;
             do
             {
                 NativeFormatModifiedType modifiedType = handle.ToModifiedTypeHandle(reader).GetModifiedType(reader);
                 if (optional == modifiedType.IsOptional)
                 {
                     Type customModifier = modifiedType.ModifierType.Resolve(reader, typeContext).ToType();
-                    customModifiers.Insert(0, customModifier);
+                    customModifiers.Add(customModifier);
                 }
 
                 handle = modifiedType.Type;
                 handleType = handle.HandleType;
             }
             while (handleType == HandleType.ModifiedType);
+            customModifiers.AsSpan().Reverse();
             return customModifiers.ToArray();
         }
 
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/TypeResolver.NativeFormat.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/TypeResolver.NativeFormat.cs
index 44be913b0195c..3aed59328d502 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/TypeResolver.NativeFormat.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/TypeResolver.NativeFormat.cs
@@ -138,7 +138,7 @@ internal static RuntimeTypeInfo ResolveTypeDefinition(this TypeDefinitionHandle
                         RuntimeTypeInfo? genericTypeDefinition = sig.GenericType.TryResolve(reader, typeContext, ref exception);
                         if (genericTypeDefinition == null)
                             return null;
-                        LowLevelList<RuntimeTypeInfo> genericTypeArguments = new LowLevelList<RuntimeTypeInfo>();
+                        ArrayBuilder<RuntimeTypeInfo> genericTypeArguments = new ArrayBuilder<RuntimeTypeInfo>(sig.GenericTypeArguments.Count);
                         foreach (Handle genericTypeArgumentHandle in sig.GenericTypeArguments)
                         {
                             RuntimeTypeInfo? genericTypeArgument = genericTypeArgumentHandle.TryResolve(reader, typeContext, ref exception);
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeGenericParameterTypeInfo.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeGenericParameterTypeInfo.cs
index a64e338004eae..c3090aa47eb10 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeGenericParameterTypeInfo.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeGenericParameterTypeInfo.cs
@@ -73,7 +73,7 @@ protected sealed override QTypeDefRefOrSpec[] Constraints
             get
             {
                 MetadataReader reader = Reader;
-                LowLevelList<QTypeDefRefOrSpec> constraints = new LowLevelList<QTypeDefRefOrSpec>();
+                ArrayBuilder<QTypeDefRefOrSpec> constraints = new ArrayBuilder<QTypeDefRefOrSpec>(_genericParameter.Constraints.Count);
                 foreach (Handle constraintHandle in _genericParameter.Constraints)
                 {
                     // We're skipping custom modifiers here because Roslyn generates
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs
index 23c0aab5638c4..65f2c3597ecc2 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs
@@ -199,7 +199,7 @@ internal sealed override RuntimeTypeInfo[] RuntimeGenericTypeParameters
         {
             get
             {
-                LowLevelList<RuntimeTypeInfo> genericTypeParameters = new LowLevelList<RuntimeTypeInfo>();
+                ArrayBuilder<RuntimeTypeInfo> genericTypeParameters = new ArrayBuilder<RuntimeTypeInfo>(_typeDefinition.GenericParameters.Count);
 
                 foreach (GenericParameterHandle genericParameterHandle in _typeDefinition.GenericParameters)
                 {
@@ -233,7 +233,7 @@ internal sealed override QTypeDefRefOrSpec[] TypeRefDefOrSpecsForDirectlyImpleme
         {
             get
             {
-                LowLevelList<QTypeDefRefOrSpec> directlyImplementedInterfaces = new LowLevelList<QTypeDefRefOrSpec>();
+                ArrayBuilder<QTypeDefRefOrSpec> directlyImplementedInterfaces = new ArrayBuilder<QTypeDefRefOrSpec>(_typeDefinition.Interfaces.Count);
                 foreach (Handle ifcHandle in _typeDefinition.Interfaces)
                     directlyImplementedInterfaces.Add(new QTypeDefRefOrSpec(_reader, ifcHandle));
                 return directlyImplementedInterfaces.ToArray();
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeGenericParameterTypeInfo.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeGenericParameterTypeInfo.cs
index 3462bde38cf7a..478193a4400c9 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeGenericParameterTypeInfo.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeGenericParameterTypeInfo.cs
@@ -152,8 +152,8 @@ internal sealed override QTypeDefRefOrSpec[] TypeRefDefOrSpecsForDirectlyImpleme
         {
             get
             {
-                LowLevelList<QTypeDefRefOrSpec> result = new LowLevelList<QTypeDefRefOrSpec>();
                 QTypeDefRefOrSpec[] constraints = Constraints;
+                ArrayBuilder<QTypeDefRefOrSpec> result = new ArrayBuilder<QTypeDefRefOrSpec>(constraints.Length);
                 RuntimeTypeInfo[] constraintInfos = ConstraintInfos;
                 for (int i = 0; i < constraints.Length; i++)
                 {
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.InvokeMember.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.InvokeMember.cs
index 5383dc1f8ed68..7a8621c1bd1e5 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.InvokeMember.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.InvokeMember.cs
@@ -266,7 +266,7 @@ internal abstract partial class RuntimeTypeInfo
             {
                 #region Lookup Methods
                 MethodInfo[] semiFinalists = (MethodInfo[])GetMember(name, MemberTypes.Method, bindingFlags);
-                LowLevelListWithIList<MethodInfo>? results = null;
+                ArrayBuilder<MethodInfo> results = default;
 
                 for (int i = 0; i < semiFinalists.Length; i++)
                 {
@@ -282,9 +282,8 @@ internal abstract partial class RuntimeTypeInfo
                     }
                     else
                     {
-                        if (results == null)
+                        if (results.Count == 0)
                         {
-                            results = new LowLevelListWithIList<MethodInfo>(semiFinalists.Length);
                             results.Add(finalist);
                         }
 
@@ -292,11 +291,9 @@ internal abstract partial class RuntimeTypeInfo
                     }
                 }
 
-                if (results != null)
+                if (results.Count > 0)
                 {
-                    Debug.Assert(results.Count > 1);
-                    finalists = new MethodInfo[results.Count];
-                    results.CopyTo(finalists, 0);
+                    finalists = results.ToArray();
                 }
                 #endregion
             }
@@ -309,7 +306,7 @@ internal abstract partial class RuntimeTypeInfo
             {
                 #region Lookup Property
                 PropertyInfo[] semiFinalists = (PropertyInfo[])GetMember(name, MemberTypes.Property, bindingFlags);
-                LowLevelListWithIList<MethodInfo>? results = null;
+                ArrayBuilder<MethodInfo> results = default;
 
                 for (int i = 0; i < semiFinalists.Length; i++)
                 {
@@ -340,9 +337,8 @@ internal abstract partial class RuntimeTypeInfo
                     }
                     else
                     {
-                        if (results == null)
+                        if (results.Count == 0)
                         {
-                            results = new LowLevelListWithIList<MethodInfo>(semiFinalists.Length);
                             results.Add(finalist);
                         }
 
@@ -350,11 +346,9 @@ internal abstract partial class RuntimeTypeInfo
                     }
                 }
 
-                if (results != null)
+                if (results.Count > 0)
                 {
-                    Debug.Assert(results.Count > 1);
-                    finalists = new MethodInfo[results.Count];
-                    results.CopyTo(finalists, 0);
+                    finalists = results.ToArray();
                 }
                 #endregion
             }
diff --git a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.MappingTables.cs b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.MappingTables.cs
index 34319199651d9..fd9fba5b7d12e 100644
--- a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.MappingTables.cs
+++ b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.MappingTables.cs
@@ -591,7 +591,7 @@ private static FunctionPointersToOffsets ComputeLdftnReverseLookup_InvokeMap(Nat
             NativeParser invokeMapParser = new NativeParser(invokeMapReader, 0);
             NativeHashtable invokeHashtable = new NativeHashtable(invokeMapParser);
 
-            LowLevelList<FunctionPointerOffsetPair> functionPointers = new LowLevelList<FunctionPointerOffsetPair>();
+            ArrayBuilder<FunctionPointerOffsetPair> functionPointers = default;
 
             var lookup = invokeHashtable.EnumerateAllEntries();
             NativeParser entryParser;
diff --git a/src/coreclr/tools/Common/Internal/LowLevelLinq/LowLevelEnumerable.ToArray.cs b/src/coreclr/tools/Common/Internal/LowLevelLinq/LowLevelEnumerable.ToArray.cs
index 6d28c01316adc..e9bb5c90898f0 100644
--- a/src/coreclr/tools/Common/Internal/LowLevelLinq/LowLevelEnumerable.ToArray.cs
+++ b/src/coreclr/tools/Common/Internal/LowLevelLinq/LowLevelEnumerable.ToArray.cs
@@ -13,12 +13,12 @@ public static T[] ToArray<T>(this IEnumerable<T> values)
         {
             Debug.Assert(values != null);
 
-            LowLevelList<T> list = new LowLevelList<T>();
+            ArrayBuilder<T> arrayBuilder = default;
             foreach (T value in values)
             {
-                list.Add(value);
+                arrayBuilder.Add(value);
             }
-            return list.ToArray();
+            return arrayBuilder.ToArray();
         }
     }
 }
diff --git a/src/coreclr/tools/Common/System/Collections/Generic/ArrayBuilder.cs b/src/coreclr/tools/Common/System/Collections/Generic/ArrayBuilder.cs
index 0005f54747827..c947e2c762ff6 100644
--- a/src/coreclr/tools/Common/System/Collections/Generic/ArrayBuilder.cs
+++ b/src/coreclr/tools/Common/System/Collections/Generic/ArrayBuilder.cs
@@ -15,6 +15,11 @@ internal struct ArrayBuilder<T>
         private T[] _items;
         private int _count;
 
+        public ArrayBuilder(int capacity)
+        {
+            _items = new T[capacity];
+        }
+
         public T[] ToArray()
         {
             if (_items == null)
@@ -24,6 +29,15 @@ public T[] ToArray()
             return _items;
         }
 
+        public void CopyTo(T[] destination)
+        {
+            if (_items != null)
+            {
+                // Use Array.Copy instead of Span.CopyTo to handle covariant destination
+                Array.Copy(_items, destination, _count);
+            }
+        }
+
         public void Add(T item)
         {
             if (_items == null || _count == _items.Length)
@@ -32,7 +46,9 @@ public void Add(T item)
         }
 
 #if NET
-        public readonly Span<T> AsSpan(int start) => _items.AsSpan(start);
+        public readonly Span<T> AsSpan() => _items.AsSpan(0, _count);
+
+        public readonly Span<T> AsSpan(int start) => _items.AsSpan(start, _count - start);
 
         public Span<T> AppendSpan(int length)
         {