diff --git a/generator/.DevConfigs/bugfix-nullable-collection-properties.json b/generator/.DevConfigs/bugfix-nullable-collection-properties.json
new file mode 100644
index 000000000000..37fd508912f6
--- /dev/null
+++ b/generator/.DevConfigs/bugfix-nullable-collection-properties.json
@@ -0,0 +1,6 @@
+{
+  "description": "Fix missing nullable annotations for collection properties in V4",
+  "versionBumpType": "patch",
+  "services": ["Core"],
+  "changelogEntry": "Fixed missing nullable reference type annotations for collection properties that can be null in V4. This enables proper compile-time null checking for Dictionary and List properties that use the AWSConfigs.InitializeCollections pattern."
+}
\ No newline at end of file
diff --git a/generator/ServiceClientGeneratorLib/Member.cs b/generator/ServiceClientGeneratorLib/Member.cs
index 53dc16ce09fb..60d99fbf7c31 100644
--- a/generator/ServiceClientGeneratorLib/Member.cs
+++ b/generator/ServiceClientGeneratorLib/Member.cs
@@ -594,11 +594,11 @@ private string DetermineType(JsonData extendedData, bool treatEnumsAsString, boo
                     bool overrideMapTreatEnumsAsString = this.model.Customizations.OverrideTreatEnumsAsString(this.Extends) ?? true;
                     var keyType = DetermineType(memberShape["key"], overrideMapTreatEnumsAsString, false);
                     var valueType = DetermineType(memberShape["value"], overrideMapTreatEnumsAsString, false);
-                    return string.Format("Dictionary<{0}, {1}>", keyType, valueType);
+                    return string.Format("Dictionary<{0}, {1}>{2}", keyType, valueType, nullable);
                 case "list":
                     bool overrideListTreatEnumsAsString = this.model.Customizations.OverrideTreatEnumsAsString(this.Extends) ?? true;
                     var listType = DetermineType(memberShape["member"], overrideListTreatEnumsAsString, false);
-                    return string.Format("List<{0}>", listType);
+                    return string.Format("List<{0}>{1}", listType, nullable);
 
                 case "decimal":
                     throw new Exception(UnhandledTypeDecimalErrorMessage);
diff --git a/sdk/src/Services/SQS/Generated/Model/SendMessageBatchResponse.cs b/sdk/src/Services/SQS/Generated/Model/SendMessageBatchResponse.cs
index 5e1d3cb9e4fd..5547d2e16e9a 100644
--- a/sdk/src/Services/SQS/Generated/Model/SendMessageBatchResponse.cs
+++ b/sdk/src/Services/SQS/Generated/Model/SendMessageBatchResponse.cs
@@ -52,7 +52,7 @@ public partial class SendMessageBatchResponse : AmazonWebServiceResponse
         /// SDK behavior set the AWSConfigs.InitializeCollections static property to true.
         /// </summary>
         [AWSProperty(Required=true)]
-        public List<BatchResultErrorEntry> Failed
+        public List<BatchResultErrorEntry>? Failed
         {
             get { return this._failed; }
             set { this._failed = value; }
@@ -76,7 +76,7 @@ internal bool IsSetFailed()
         /// SDK behavior set the AWSConfigs.InitializeCollections static property to true.
         /// </summary>
         [AWSProperty(Required=true)]
-        public List<SendMessageBatchResultEntry> Successful
+        public List<SendMessageBatchResultEntry>? Successful
         {
             get { return this._successful; }
             set { this._successful = value; }