diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java
index 4d7eb4dbe7c1..4389714fa119 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractDartCodegen.java
@@ -622,6 +622,7 @@ public ModelsMap postProcessModels(ModelsMap objs) {
         if (useOptional) {
             for (ModelMap modelMap : objs.getModels()) {
                 CodegenModel model = modelMap.getModel();
+                boolean hasOptionalProperties = false;
 
                 boolean shouldUseOptional;
 
@@ -636,9 +637,12 @@ public ModelsMap postProcessModels(ModelsMap objs) {
                     for (CodegenProperty prop : model.vars) {
                         if (!prop.required && !prop.dataType.startsWith("Optional<")) {
                             wrapPropertyWithOptional(prop);
+                            hasOptionalProperties = true;
                         }
                     }
                 }
+
+                model.vendorExtensions.put("x-has-optional-properties", hasOptionalProperties);
             }
         }
 
@@ -653,6 +657,7 @@ private void wrapPropertyWithOptional(CodegenProperty property) {
 
         boolean hasNullableSuffix = property.dataType.endsWith("?");
         String baseType = hasNullableSuffix ? property.dataType.substring(0, property.dataType.length() - 1) : property.dataType;
+        property.vendorExtensions.put("x-unwrapped-datatype-nullable", baseType + "?");
         property.dataType = "Optional<" + baseType + "?" + ">";
 
         if (property.datatypeWithEnum != null && !property.datatypeWithEnum.startsWith("Optional<")) {
@@ -660,6 +665,8 @@ private void wrapPropertyWithOptional(CodegenProperty property) {
             baseType = hasNullableSuffix ? property.datatypeWithEnum.substring(0, property.datatypeWithEnum.length() - 1) : property.datatypeWithEnum;
             property.datatypeWithEnum = "Optional<" + baseType + "?" + ">";
         }
+
+        property.isNullable = false;
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/lib.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/lib.mustache
index 880bb6258354..581624c15a8b 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/lib.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/lib.mustache
@@ -4,6 +4,8 @@ export 'package:{{pubName}}/{{sourceFolder}}/auth/api_key_auth.dart';
 export 'package:{{pubName}}/{{sourceFolder}}/auth/basic_auth.dart';
 export 'package:{{pubName}}/{{sourceFolder}}/auth/bearer_auth.dart';
 export 'package:{{pubName}}/{{sourceFolder}}/auth/oauth.dart';
+{{#useOptional}}export 'package:{{pubName}}/{{sourceFolder}}/optional.dart';
+{{/useOptional}}
 {{#useBuiltValue}}export 'package:{{pubName}}/{{sourceFolder}}/serializers.dart';
 {{#useDateLibCore}}export 'package:{{pubName}}/{{sourceFolder}}/{{modelPackage}}/date.dart';{{/useDateLibCore}}{{/useBuiltValue}}
 
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/optional.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/optional.mustache
index 9a2747da4e52..f4fa6f8f2586 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/optional.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/optional.mustache
@@ -19,7 +19,7 @@ import 'package:json_annotation/json_annotation.dart';
 /// // Field has value - sends {"field": "value"}
 /// final patch3 = Model(field: const Optional.present('value'));
 /// ```
-sealed class Optional<T> {
+abstract class Optional<T> {
   const Optional();
 
   /// Creates an Optional with an absent value (not set).
@@ -48,7 +48,7 @@ sealed class Optional<T> {
 }
 
 /// Represents an absent Optional value.
-final class Absent<T> extends Optional<T> {
+class Absent<T> extends Optional<T> {
   const Absent();
 
   @override
@@ -77,7 +77,7 @@ final class Absent<T> extends Optional<T> {
 }
 
 /// Represents a present Optional value.
-final class Present<T> extends Optional<T> {
+class Present<T> extends Optional<T> {
   const Present(this._value);
 
   final T _value;
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class.mustache
index 7a9ee688596b..b7ce07ace304 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class.mustache
@@ -2,6 +2,8 @@ import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';{{#oneOf}}{{#-first}}
 import 'package:one_of/one_of.dart';{{/-first}}{{/oneOf}}{{#anyOf}}{{#-first}}
 import 'package:one_of/any_of.dart';{{/-first}}{{/anyOf}}
+{{#vendorExtensions.x-has-optional-properties}}import 'package:{{pubName}}/{{sourceFolder}}/optional.dart';
+{{/vendorExtensions.x-has-optional-properties}}
 
 {{#imports}}
 {{/imports}}
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_members.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_members.mustache
index 50b7f98ba60d..cfc50dd82b87 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_members.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_members.mustache
@@ -7,7 +7,7 @@
   @Deprecated('{{{name}}} has been deprecated')
   {{/deprecated}}
   @BuiltValueField(wireName: r'{{baseName}}')
-  {{>serialization/built_value/variable_type}}{{^isNullable}}{{^required}}?{{/required}}{{/isNullable}} get {{name}};
+  {{>serialization/built_value/variable_type}}{{^vendorExtensions.x-is-optional}}{{^isNullable}}{{^required}}?{{/required}}{{/isNullable}}{{/vendorExtensions.x-is-optional}} get {{name}};
   {{#allowableValues}}
   // {{#min}}range from {{{min}}} to {{{max}}}{{/min}}{{^min}}enum {{name}}Enum { {{#values}} {{{.}}}, {{/values}} };{{/min}}
   {{/allowableValues}}
@@ -31,8 +31,9 @@
   factory {{classname}}([void updates({{classname}}Builder b)]) = _${{classname}};
 
   @BuiltValueHook(initializeBuilder: true)
-  static void _defaults({{{classname}}}Builder b) => b{{#vendorExtensions.x-parent-discriminator}}..{{propertyName}}=b.discriminatorValue{{/vendorExtensions.x-parent-discriminator}}{{#vendorExtensions.x-self-and-ancestor-only-props}}{{#defaultValue}}
-      ..{{{name}}} = {{#isEnum}}{{^isContainer}}{{#enumName}}{{enumName}}.valueOf({{{defaultValue}}}){{/enumName}}{{^enumName}}{{{defaultValue}}}{{/enumName}}{{/isContainer}}{{/isEnum}}{{^isEnum}}{{{defaultValue}}}{{/isEnum}}{{/defaultValue}}{{/vendorExtensions.x-self-and-ancestor-only-props}};
+  static void _defaults({{{classname}}}Builder b) => b{{#vendorExtensions.x-parent-discriminator}}..{{propertyName}}=b.discriminatorValue{{/vendorExtensions.x-parent-discriminator}}{{#vendorExtensions.x-self-and-ancestor-only-props}}{{#vendorExtensions.x-is-optional}}
+      ..{{{name}}} = Optional.absent(){{/vendorExtensions.x-is-optional}}{{^vendorExtensions.x-is-optional}}{{#defaultValue}}
+      ..{{{name}}} = {{#isEnum}}{{^isContainer}}{{#enumName}}{{enumName}}.valueOf({{{defaultValue}}}){{/enumName}}{{^enumName}}{{{defaultValue}}}{{/enumName}}{{/isContainer}}{{/isEnum}}{{^isEnum}}{{{defaultValue}}}{{/isEnum}}{{/defaultValue}}{{/vendorExtensions.x-is-optional}}{{/vendorExtensions.x-self-and-ancestor-only-props}};
 
 {{/vendorExtensions.x-is-parent}}  @BuiltValueSerializer(custom: true)
   static Serializer<{{classname}}> get serializer => _${{classname}}Serializer();
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_serializer.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_serializer.mustache
index 4cd02f3506de..ef0a6301bfa3 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_serializer.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/class_serializer.mustache
@@ -11,6 +11,21 @@ class _${{classname}}Serializer implements PrimitiveSerializer<{{classname}}> {
     FullType specifiedType = FullType.unspecified,
   }) sync* {
     {{#vendorExtensions.x-self-and-ancestor-only-props}}
+    {{#vendorExtensions.x-is-optional}}
+    if (object.{{{name}}}.isPresent) {
+      yield r'{{baseName}}';
+      final optionalValue = object.{{{name}}}.value;
+      if (optionalValue == null) {
+        yield null;
+      } else {
+        yield serializers.serialize(
+          optionalValue,
+          specifiedType: const {{>serialization/built_value/variable_serializer_type}},
+        );
+      }
+    }
+    {{/vendorExtensions.x-is-optional}}
+    {{^vendorExtensions.x-is-optional}}
     {{#required}}
     {{!
         A required property need to always be part of the serialized output.
@@ -32,6 +47,7 @@ class _${{classname}}Serializer implements PrimitiveSerializer<{{classname}}> {
       );
     }
     {{/required}}
+    {{/vendorExtensions.x-is-optional}}
     {{/vendorExtensions.x-self-and-ancestor-only-props}}
   }
 
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/deserialize_properties.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/deserialize_properties.mustache
index d64ec8086c34..b04145f5b5a8 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/deserialize_properties.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/deserialize_properties.mustache
@@ -12,6 +12,14 @@
       switch (key) {
         {{#vendorExtensions.x-self-and-ancestor-only-props}}
         case r'{{baseName}}':
+          {{#vendorExtensions.x-is-optional}}
+          final valueDes = serializers.deserialize(
+            value,
+            specifiedType: const {{>serialization/built_value/variable_serializer_type}},
+          ) as {{{vendorExtensions.x-unwrapped-datatype-nullable}}};
+          result.{{{name}}} = Optional.present(valueDes);
+          {{/vendorExtensions.x-is-optional}}
+          {{^vendorExtensions.x-is-optional}}
           final valueDes = serializers.deserialize(
             value,
             specifiedType: const {{>serialization/built_value/variable_serializer_type}},
@@ -46,6 +54,7 @@
           {{/isModel}}
           {{/isEnum}}
           {{/isContainer}}
+          {{/vendorExtensions.x-is-optional}}
           break;
         {{/vendorExtensions.x-self-and-ancestor-only-props}}
         default:
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_serializer_type.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_serializer_type.mustache
index c76dde39a9c9..8116fcb4ede8 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_serializer_type.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_serializer_type.mustache
@@ -1 +1 @@
-FullType{{#isNullable}}.nullable{{/isNullable}}({{#isContainer}}{{baseType}}, [{{#isMap}}FullType(String), {{/isMap}}{{#items}}{{>serialization/built_value/variable_serializer_type}}{{/items}}]{{/isContainer}}{{^isContainer}}{{{datatypeWithEnum}}}{{/isContainer}})
\ No newline at end of file
+{{#vendorExtensions.x-is-optional}}{{#isContainer}}FullType{{#isNullable}}.nullable{{/isNullable}}({{baseType}}, [{{#isMap}}FullType(String), {{/isMap}}{{#items}}{{>serialization/built_value/variable_serializer_type}}{{/items}}]){{/isContainer}}{{^isContainer}}FullType.nullable({{{vendorExtensions.x-unwrapped-datatype}}}){{/isContainer}}{{/vendorExtensions.x-is-optional}}{{^vendorExtensions.x-is-optional}}FullType{{#isNullable}}.nullable{{/isNullable}}({{#isContainer}}{{baseType}}, [{{#isMap}}FullType(String), {{/isMap}}{{#items}}{{>serialization/built_value/variable_serializer_type}}{{/items}}]{{/isContainer}}{{^isContainer}}{{{datatypeWithEnum}}}{{/isContainer}}){{/vendorExtensions.x-is-optional}}
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_type.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_type.mustache
index 136545525cac..78ca08f2a1c6 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_type.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/variable_type.mustache
@@ -1 +1 @@
-{{#isContainer}}{{baseType}}<{{#isMap}}String, {{/isMap}}{{#items}}{{>serialization/built_value/variable_type}}{{/items}}>{{/isContainer}}{{^isContainer}}{{{datatypeWithEnum}}}{{/isContainer}}{{#isNullable}}?{{/isNullable}}
\ No newline at end of file
+{{#isContainer}}{{baseType}}<{{#isMap}}String, {{/isMap}}{{#items}}{{>serialization/built_value/variable_type}}{{/items}}>{{/isContainer}}{{^isContainer}}{{{datatypeWithEnum}}}{{/isContainer}}{{#isNullable}}{{^vendorExtensions.x-is-optional}}?{{/vendorExtensions.x-is-optional}}{{/isNullable}}
\ No newline at end of file