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 bd3a854f39a64f..719908065cbe5d 100644
--- a/src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelList.cs
+++ b/src/coreclr/nativeaot/Common/src/System/Collections/Generic/LowLevelList.cs
@@ -4,16 +4,18 @@
 /*============================================================
 **
 **
-** Private version of List<T> for internal System.Private.CoreLib use. This
-** permits sharing more source between BCL and System.Private.CoreLib (as well as the
-** fact that List<T> is just a useful class in general.)
+** Private version of List<T> for internal System.Private.TypeLoader use. Type
+** loader itself can't use generic types without [ForceDictionaryLookups], and
+** we don't want to annotate List<T> with it because it would impact size and
+** performance for general usages.
 **
 ** This does not strive to implement the full api surface area
 ** (but any portion it does implement should match the real List<T>'s
 ** behavior.)
 **
-** This file is a subset of System.Collections\System\Collections\Generics\List.cs
-** and should be kept in sync with that file.
+** This file is a subset of
+** src\libraries\System.Private.CoreLib\src\System\Collections\Generics\List.cs
+** and should be kept in sync with that file when necessary.
 **
 ===========================================================*/
 
@@ -32,16 +34,14 @@ namespace System.Collections.Generic
     // 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.
     [DebuggerDisplay("Count = {Count}")]
-#if TYPE_LOADER_IMPLEMENTATION
     [System.Runtime.CompilerServices.ForceDictionaryLookups]
-#endif
     internal class LowLevelList<T>
     {
         private const int _defaultCapacity = 4;
 
         protected T[] _items;
         protected int _size;
-        protected int _version;
+        // No _version field because no IEnumerable<T> support
 
 #pragma warning disable CA1825 // avoid the extra generic instantiation for Array.Empty<T>()
         private static readonly T[] s_emptyArray = new T[0];
@@ -55,60 +55,6 @@ public LowLevelList()
             _items = s_emptyArray;
         }
 
-        // Constructs a List with a given initial capacity. The list is
-        // initially empty, but will have room for the given number of elements
-        // before any reallocations are required.
-        //
-        public LowLevelList(int capacity)
-        {
-            ArgumentOutOfRangeException.ThrowIfNegative(capacity);
-
-            if (capacity == 0)
-                _items = s_emptyArray;
-            else
-                _items = new T[capacity];
-        }
-
-        // Constructs a List, copying the contents of the given collection. The
-        // size and capacity of the new list will both be equal to the size of the
-        // given collection.
-        //
-        public LowLevelList(IEnumerable<T> collection)
-        {
-            ArgumentNullException.ThrowIfNull(collection);
-
-            ICollection<T>? c = collection as ICollection<T>;
-            if (c != null)
-            {
-                int count = c.Count;
-                if (count == 0)
-                {
-                    _items = s_emptyArray;
-                }
-                else
-                {
-                    _items = new T[count];
-                    c.CopyTo(_items, 0);
-                    _size = count;
-                }
-            }
-            else
-            {
-                _size = 0;
-                _items = s_emptyArray;
-                // This enumerable could be empty.  Let Add allocate a new array, if needed.
-                // Note it will also go to _defaultCapacity first, not 1, then 2, etc.
-
-                using (IEnumerator<T> en = collection.GetEnumerator())
-                {
-                    while (en.MoveNext())
-                    {
-                        Add(en.Current);
-                    }
-                }
-            }
-        }
-
         // Gets and sets the capacity of this list.  The capacity is the size of
         // the internal array used to hold items.  When set, the internal
         // array of the list is reallocated to the given capacity.
@@ -163,7 +109,6 @@ public T this[int index]
             {
                 ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual((uint)index, (uint)_size, nameof(index));
                 _items[index] = value;
-                _version++;
             }
         }
 
@@ -176,7 +121,6 @@ public void Add(T item)
         {
             if (_size == _items.Length) EnsureCapacity(_size + 1);
             _items[_size++] = item;
-            _version++;
         }
 
         // Ensures that the capacity of this list is at least the given minimum
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Reflection/Extensions/NonPortable/CustomAttributeSearcher.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Reflection/Extensions/NonPortable/CustomAttributeSearcher.cs
index 89ede0e6d92fe8..4720d0caf8a2e3 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Reflection/Extensions/NonPortable/CustomAttributeSearcher.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Reflection/Extensions/NonPortable/CustomAttributeSearcher.cs
@@ -120,7 +120,7 @@ private IEnumerable<CustomAttributeData> GetMatchingCustomAttributesIterator(E e
                     return rawPassesFilter(attributeType);
                 };
 
-            LowLevelList<CustomAttributeData> immediateResults = new LowLevelList<CustomAttributeData>();
+            List<CustomAttributeData> immediateResults = new List<CustomAttributeData>();
             foreach (CustomAttributeData cad in GetDeclaredCustomAttributes(element))
             {
                 if (passesFilter(cad.AttributeType))
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/FunctionPointerOps.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/FunctionPointerOps.cs
index c0bceb7963c8ad..96e2b8b1cbd449 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/FunctionPointerOps.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/FunctionPointerOps.cs
@@ -51,7 +51,7 @@ public override int GetHashCode()
 
         private static uint s_genericFunctionPointerNextIndex;
         private const uint c_genericDictionaryChunkSize = 1024;
-        private static LowLevelList<IntPtr> s_genericFunctionPointerCollection = new LowLevelList<IntPtr>();
+        private static readonly List<IntPtr> s_genericFunctionPointerCollection = new List<IntPtr>();
         private static LowLevelDictionary<GenericMethodDescriptorInfo, uint> s_genericFunctionPointerDictionary = new LowLevelDictionary<GenericMethodDescriptorInfo, uint>();
 
         public static unsafe IntPtr GetGenericMethodFunctionPointer(IntPtr canonFunctionPointer, IntPtr instantiationArgument)
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
index 72df9073427635..6b769818faf42e 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
@@ -329,9 +329,6 @@
     <Compile Include="$(CompilerCommonPath)\TypeSystem\Common\Utilities\LockFreeReaderHashtableOfPointers.cs">
       <Link>Utilities\LockFreeReaderHashtableOfPointers.cs</Link>
     </Compile>
-    <Compile Include="$(AotCommonPath)\System\Collections\Generic\LowLevelList.cs">
-      <Link>System\Collections\Generic\LowLevelList.cs</Link>
-    </Compile>
     <Compile Include="$(AotCommonPath)\System\Collections\Generic\LowLevelDictionary.cs">
       <Link>System\Collections\Generic\LowLevelDictionary.cs</Link>
     </Compile>
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/NamespaceChain.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/NamespaceChain.cs
index ff812387e04ddc..ce53181af13e72 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/NamespaceChain.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/NamespaceChain.cs
@@ -22,7 +22,7 @@ internal NamespaceChain(MetadataReader reader, NamespaceDefinitionHandle innerMo
             NamespaceDefinition currentNamespaceDefinition = innerMostNamespaceHandle.GetNamespaceDefinition(reader);
             ConstantStringValueHandle currentNameHandle = currentNamespaceDefinition.Name;
             Handle currentNamespaceHandle;
-            LowLevelList<string> names = new LowLevelList<string>();
+            List<string> names = new List<string>();
             for (; ; )
             {
                 string name = currentNameHandle.GetStringOrNull(reader);
diff --git a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.ManifestResources.cs b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.ManifestResources.cs
index 182a3333d6a9d0..2b3a0e624f94c0 100644
--- a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.ManifestResources.cs
+++ b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.ManifestResources.cs
@@ -22,7 +22,7 @@ internal sealed partial class ExecutionEnvironmentImplementation : ExecutionEnvi
     {
         public sealed override ManifestResourceInfo GetManifestResourceInfo(Assembly assembly, string resourceName)
         {
-            LowLevelList<ResourceInfo> resourceInfos = GetExtractedResources(assembly);
+            List<ResourceInfo> resourceInfos = GetExtractedResources(assembly);
             for (int i = 0; i < resourceInfos.Count; i++)
             {
                 if (resourceName == resourceInfos[i].Name)
@@ -35,7 +35,7 @@ public sealed override ManifestResourceInfo GetManifestResourceInfo(Assembly ass
 
         public sealed override string[] GetManifestResourceNames(Assembly assembly)
         {
-            LowLevelList<ResourceInfo> resourceInfos = GetExtractedResources(assembly);
+            List<ResourceInfo> resourceInfos = GetExtractedResources(assembly);
             string[] names = new string[resourceInfos.Count];
             for (int i = 0; i < resourceInfos.Count; i++)
             {
@@ -50,7 +50,7 @@ public sealed override Stream GetManifestResourceStream(Assembly assembly, strin
 
             // This was most likely an embedded resource which the toolchain should have embedded
             // into an assembly.
-            LowLevelList<ResourceInfo> resourceInfos = GetExtractedResources(assembly);
+            List<ResourceInfo> resourceInfos = GetExtractedResources(assembly);
             for (int i = 0; i < resourceInfos.Count; i++)
             {
                 ResourceInfo resourceInfo = resourceInfos[i];
@@ -78,17 +78,17 @@ private static unsafe UnmanagedMemoryStream ReadResourceFromBlob(ResourceInfo re
             return new UnmanagedMemoryStream(pBlob + resourceInfo.Index, resourceInfo.Length);
         }
 
-        private static LowLevelList<ResourceInfo> GetExtractedResources(Assembly assembly)
+        private static List<ResourceInfo> GetExtractedResources(Assembly assembly)
         {
-            LowLevelDictionary<string, LowLevelList<ResourceInfo>> extractedResourceDictionary = ExtractedResourceDictionary;
+            Dictionary<string, List<ResourceInfo>> extractedResourceDictionary = ExtractedResourceDictionary;
             string assemblyName = assembly.GetName().FullName;
-            LowLevelList<ResourceInfo> resourceInfos;
+            List<ResourceInfo> resourceInfos;
             if (!extractedResourceDictionary.TryGetValue(assemblyName, out resourceInfos))
-                return new LowLevelList<ResourceInfo>();
+                return new List<ResourceInfo>();
             return resourceInfos;
         }
 
-        private static LowLevelDictionary<string, LowLevelList<ResourceInfo>> ExtractedResourceDictionary
+        private static Dictionary<string, List<ResourceInfo>> ExtractedResourceDictionary
         {
             get
             {
@@ -97,7 +97,7 @@ private static LowLevelDictionary<string, LowLevelList<ResourceInfo>> ExtractedR
                     // Lazily create the extracted resource dictionary. If two threads race here, we may construct two dictionaries
                     // and overwrite one - this is ok since the dictionaries are read-only once constructed and they contain the identical data.
 
-                    LowLevelDictionary<string, LowLevelList<ResourceInfo>> dict = new LowLevelDictionary<string, LowLevelList<ResourceInfo>>();
+                    Dictionary<string, List<ResourceInfo>> dict = new Dictionary<string, List<ResourceInfo>>();
 
                     foreach (NativeFormatModuleInfo module in ModuleList.EnumerateModules())
                     {
@@ -120,10 +120,10 @@ private static LowLevelDictionary<string, LowLevelList<ResourceInfo>> ExtractedR
 
                             ResourceInfo resourceInfo = new ResourceInfo(resourceName, resourceOffset, resourceLength, module);
 
-                            LowLevelList<ResourceInfo> assemblyResources;
+                            List<ResourceInfo> assemblyResources;
                             if (!dict.TryGetValue(assemblyName, out assemblyResources))
                             {
-                                assemblyResources = new LowLevelList<ResourceInfo>();
+                                assemblyResources = new List<ResourceInfo>();
                                 dict[assemblyName] = assemblyResources;
                             }
 
@@ -144,7 +144,7 @@ private static LowLevelDictionary<string, LowLevelList<ResourceInfo>> ExtractedR
         /// The dictionary's key is a Fusion-style assembly name.
         /// The dictionary's value is a list of (resourcename,index) tuples.
         /// </summary>
-        private static volatile LowLevelDictionary<string, LowLevelList<ResourceInfo>> s_extractedResourceDictionary;
+        private static volatile Dictionary<string, List<ResourceInfo>> s_extractedResourceDictionary;
 
         private struct ResourceInfo
         {
diff --git a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/System.Private.Reflection.Execution.csproj b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/System.Private.Reflection.Execution.csproj
index 86fb64fa51852c..6f76fdb352a3fa 100644
--- a/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/System.Private.Reflection.Execution.csproj
+++ b/src/coreclr/nativeaot/System.Private.Reflection.Execution/src/System.Private.Reflection.Execution.csproj
@@ -56,9 +56,6 @@
       <Link>System\NotImplemented.cs</Link>
     </Compile>
     <Compile Include="$(LibrariesProjectRoot)\System.Private.CoreLib\src\System\SR.cs" />
-    <Compile Include="$(AotCommonPath)\System\Collections\Generic\LowLevelList.cs">
-      <Link>System\Collections\Generic\LowLevelList.cs</Link>
-    </Compile>
     <Compile Include="$(AotCommonPath)\System\Collections\Generic\LowLevelDictionary.cs">
       <Link>System\Collections\Generic\LowLevelDictionary.cs</Link>
     </Compile>
diff --git a/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs b/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs
index 9a5995e17fb9ef..a4474f8d7f4b07 100644
--- a/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs
+++ b/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs
@@ -457,9 +457,9 @@ private static unsafe int GetInstanceGCDescSize(TypeBuilderState state, MethodTa
             }
         }
 
-        private static bool IsAllGCPointers(LowLevelList<bool> bitfield)
+        private static bool IsAllGCPointers(bool[] bitfield)
         {
-            int count = bitfield.Count;
+            int count = bitfield.Length;
             Debug.Assert(count > 0);
 
             for (int i = 0; i < count; i++)
@@ -471,7 +471,7 @@ private static bool IsAllGCPointers(LowLevelList<bool> bitfield)
             return true;
         }
 
-        private static unsafe int CreateArrayGCDesc(LowLevelList<bool> bitfield, int rank, bool isSzArray, void* gcdesc)
+        private static unsafe int CreateArrayGCDesc(bool[] bitfield, int rank, bool isSzArray, void* gcdesc)
         {
             if (bitfield == null)
                 return 0;
@@ -495,7 +495,7 @@ private static unsafe int CreateArrayGCDesc(LowLevelList<bool> bitfield, int ran
             int first = -1;
             int last = 0;
             short numPtrs = 0;
-            while (i < bitfield.Count)
+            while (i < bitfield.Length)
             {
                 if (bitfield[i])
                 {
@@ -513,7 +513,7 @@ private static unsafe int CreateArrayGCDesc(LowLevelList<bool> bitfield, int ran
                     numSeries++;
                     numPtrs = 0;
 
-                    while ((i < bitfield.Count) && (bitfield[i]))
+                    while ((i < bitfield.Length) && (bitfield[i]))
                     {
                         numPtrs++;
                         i++;
@@ -531,7 +531,7 @@ private static unsafe int CreateArrayGCDesc(LowLevelList<bool> bitfield, int ran
             {
                 if (numSeries > 0)
                 {
-                    *ptr-- = (short)((first + bitfield.Count - last) * IntPtr.Size);
+                    *ptr-- = (short)((first + bitfield.Length - last) * IntPtr.Size);
                     *ptr-- = numPtrs;
 
                     *(void**)gcdesc = (void*)-numSeries;
@@ -542,7 +542,7 @@ private static unsafe int CreateArrayGCDesc(LowLevelList<bool> bitfield, int ran
             return numSeries;
         }
 
-        private static unsafe int CreateGCDesc(LowLevelList<bool> bitfield, int size, bool isValueType, bool isStatic, void* gcdesc)
+        private static unsafe int CreateGCDesc(bool[] bitfield, int size, bool isValueType, bool isStatic, void* gcdesc)
         {
             int offs = 0;
             // if this type is a class we have to account for the gcdesc.
@@ -558,7 +558,7 @@ private static unsafe int CreateGCDesc(LowLevelList<bool> bitfield, int size, bo
 
             int numSeries = 0;
             int i = 0;
-            while (i < bitfield.Count)
+            while (i < bitfield.Length)
             {
                 if (bitfield[i])
                 {
@@ -566,7 +566,7 @@ private static unsafe int CreateGCDesc(LowLevelList<bool> bitfield, int size, bo
                     int seriesOffset = i * IntPtr.Size + offs;
                     int seriesSize = 0;
 
-                    while ((i < bitfield.Count) && (bitfield[i]))
+                    while ((i < bitfield.Length) && (bitfield[i]))
                     {
                         seriesSize += IntPtr.Size;
                         i++;
diff --git a/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilder.cs b/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilder.cs
index 48bb6c91b6169d..3af4f4451db7c0 100644
--- a/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilder.cs
+++ b/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilder.cs
@@ -13,18 +13,6 @@
 
 namespace Internal.Runtime.TypeLoader
 {
-    internal static class LowLevelListExtensions
-    {
-        public static void Expand<T>(this LowLevelList<T> list, int count)
-        {
-            if (list.Capacity < count)
-                list.Capacity = count;
-
-            while (list.Count < count)
-                list.Add(default(T));
-        }
-    }
-
     internal class TypeBuilder
     {
         public TypeBuilder()
@@ -447,17 +435,17 @@ internal void ParseNativeLayoutInfo(TypeBuilderState state, TypeDesc type)
         /// </summary>
         internal unsafe struct GCLayout
         {
-            private LowLevelList<bool> _bitfield;
+            private bool[] _bitfield;
             private unsafe void* _gcdesc;
             private int _size;
             private bool _isReferenceTypeGCLayout;
 
             public static GCLayout None { get { return default(GCLayout); } }
-            public static GCLayout SingleReference { get; } = new GCLayout(new LowLevelList<bool>(new bool[1] { true }), false);
+            public static GCLayout SingleReference { get; } = new GCLayout([true], false);
 
             public bool IsNone { get { return _bitfield == null && _gcdesc == null; } }
 
-            public GCLayout(LowLevelList<bool> bitfield, bool isReferenceTypeGCLayout)
+            public GCLayout(bool[] bitfield, bool isReferenceTypeGCLayout)
             {
                 Debug.Assert(bitfield != null);
 
@@ -473,7 +461,7 @@ public GCLayout(RuntimeTypeHandle rtth)
                 Debug.Assert(MethodTable != null);
 
                 _bitfield = null;
-                _isReferenceTypeGCLayout = false; // This field is only used for the LowLevelList<bool> path
+                _isReferenceTypeGCLayout = false; // This field is only used for the bool[] path
                 _gcdesc = MethodTable->ContainsGCPointers ? (void**)MethodTable - 1 : null;
                 _size = (int)MethodTable->BaseSize;
             }
@@ -481,29 +469,21 @@ public GCLayout(RuntimeTypeHandle rtth)
             /// <summary>
             /// Writes this layout to the given bitfield.
             /// </summary>
-            /// <param name="bitfield">The bitfield to write a layout to (may be null, at which
-            /// point it will be created and assigned).</param>
-            /// <param name="offset">The offset at which we need to write the bitfield.</param>
-            public void WriteToBitfield(LowLevelList<bool> bitfield, int offset)
+            /// <returns>The result bitfield.</returns>
+            public bool[] WriteToBitfield()
             {
-                ArgumentNullException.ThrowIfNull(bitfield);
-
-                if (IsNone)
-                    return;
-
                 // Ensure exactly one of these two are set.
+                Debug.Assert(!IsNone);
                 Debug.Assert(_gcdesc != null ^ _bitfield != null);
 
                 if (_bitfield != null)
-                    MergeBitfields(bitfield, offset);
+                    return MergeBitfields();
                 else
-                    WriteGCDescToBitfield(bitfield, offset);
+                    return WriteGCDescToBitfield();
             }
 
-            private unsafe void WriteGCDescToBitfield(LowLevelList<bool> bitfield, int offset)
+            private unsafe bool[] WriteGCDescToBitfield()
             {
-                int startIndex = offset / IntPtr.Size;
-
                 void** ptr = (void**)_gcdesc;
                 Debug.Assert(_gcdesc != null);
 
@@ -512,8 +492,8 @@ private unsafe void WriteGCDescToBitfield(LowLevelList<bool> bitfield, int offse
                 Debug.Assert(count >= 0);
 
                 // Ensure capacity for the values we are about to write
-                int capacity = startIndex + _size / IntPtr.Size - 2;
-                bitfield.Expand(capacity);
+                int capacity = _size / IntPtr.Size - 2;
+                bool[] bitfield = new bool[capacity];
 
                 while (count-- >= 0)
                 {
@@ -524,35 +504,35 @@ private unsafe void WriteGCDescToBitfield(LowLevelList<bool> bitfield, int offse
                     Debug.Assert(offs >= 0);
 
                     for (int i = 0; i < len; i++)
-                        bitfield[startIndex + offs + i] = true;
+                        bitfield[offs + i] = true;
                 }
+
+                return bitfield;
             }
 
-            private void MergeBitfields(LowLevelList<bool> outputBitfield, int offset)
+            private bool[] MergeBitfields()
             {
-                int startIndex = offset / IntPtr.Size;
-
                 // These routines represent the GC layout after the MethodTable pointer
-                // in an object, but the LowLevelList<bool> bitfield logically contains
-                // the EETypepointer if it is describing a reference type. So, skip the
-                // first value.
+                // in an object, but the bool[] bitfield logically contains the EETypepointer
+                // if it is describing a reference type. So, skip the first value.
                 int itemsToSkip = _isReferenceTypeGCLayout ? 1 : 0;
 
                 // Assert that we only skip a non-reported pointer.
                 Debug.Assert(itemsToSkip == 0 || _bitfield[0] == false);
 
                 // Ensure capacity for the values we are about to write
-                int capacity = startIndex + _bitfield.Count - itemsToSkip;
-                outputBitfield.Expand(capacity);
-
+                int capacity = _bitfield.Length - itemsToSkip;
+                bool[] outputBitfield = new bool[capacity];
 
-                for (int i = itemsToSkip; i < _bitfield.Count; i++)
+                for (int i = itemsToSkip; i < _bitfield.Length; i++)
                 {
                     // We should never overwrite a TRUE value in the table.
-                    Debug.Assert(!outputBitfield[startIndex + i - itemsToSkip] || _bitfield[i]);
+                    Debug.Assert(!outputBitfield[i - itemsToSkip] || _bitfield[i]);
 
-                    outputBitfield[startIndex + i - itemsToSkip] = _bitfield[i];
+                    outputBitfield[i - itemsToSkip] = _bitfield[i];
                 }
+
+                return outputBitfield;
             }
         }
 
diff --git a/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs b/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs
index 39915c06576a15..5d903501773f84 100644
--- a/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs
+++ b/src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs
@@ -306,9 +306,11 @@ public ushort NumVTableSlots
 
         // Sentinel static to allow us to initialize _instanceLayout to something
         // and then detect that InstanceGCLayout should return null
-        private static LowLevelList<bool> s_emptyLayout = new LowLevelList<bool>();
+#pragma warning disable CA1825 // Can't use generic Array.Empty<T> within type loader
+        private static bool[] s_emptyLayout = new bool[0];
+#pragma warning restore CA1825
 
-        private LowLevelList<bool> _instanceGCLayout;
+        private bool[] _instanceGCLayout;
 
         /// <summary>
         /// The instance gc layout of a dynamically laid out type.
@@ -324,14 +326,12 @@ public ushort NumVTableSlots
         /// If the type is a valuetype array, this is the layout of the valuetype held in the array if the type has GC reference fields
         /// Otherwise, it is the layout of the fields in the type.
         /// </summary>
-        public LowLevelList<bool> InstanceGCLayout
+        public bool[] InstanceGCLayout
         {
             get
             {
                 if (_instanceGCLayout == null)
                 {
-                    LowLevelList<bool> instanceGCLayout;
-
                     if (TypeBeingBuilt is ArrayType)
                     {
                         if (!IsArrayOfReferenceTypes)
@@ -340,9 +340,7 @@ public LowLevelList<bool> InstanceGCLayout
                             TypeBuilder.GCLayout elementGcLayout = GetFieldGCLayout(arrayType.ElementType);
                             if (!elementGcLayout.IsNone)
                             {
-                                instanceGCLayout = new LowLevelList<bool>();
-                                elementGcLayout.WriteToBitfield(instanceGCLayout, 0);
-                                _instanceGCLayout = instanceGCLayout;
+                                _instanceGCLayout = elementGcLayout.WriteToBitfield();
                             }
                         }
                         else