diff --git a/sagemaker-core/src/sagemaker/core/resources.py b/sagemaker-core/src/sagemaker/core/resources.py
index 19a314fc3f..a780c829eb 100644
--- a/sagemaker-core/src/sagemaker/core/resources.py
+++ b/sagemaker-core/src/sagemaker/core/resources.py
@@ -22984,7 +22984,11 @@ def refresh(
         """
 
         operation_input_args = {
-            "ModelPackageName": self.model_package_name,
+            "ModelPackageName": (
+                self.model_package_name
+                if not isinstance(self.model_package_name, Unassigned)
+                else self.model_package_arn
+            ),
         }
         # serialize the input request
         operation_input_args = serialize(operation_input_args)
diff --git a/sagemaker-core/src/sagemaker/core/tools/resources_codegen.py b/sagemaker-core/src/sagemaker/core/tools/resources_codegen.py
index d6cc9ba325..27b5ccea8c 100644
--- a/sagemaker-core/src/sagemaker/core/tools/resources_codegen.py
+++ b/sagemaker-core/src/sagemaker/core/tools/resources_codegen.py
@@ -98,6 +98,14 @@
 REQUIRED = "required"
 GLOBAL_DEFAULTS = "GlobalDefaults"
 
+# Some resources do not return their *Name identifier from the List API for certain
+# variants (e.g. a versioned ModelPackage returns only ModelPackageArn). Because the
+# Describe API accepts either the name or the ARN for the *Name parameter, refresh()
+# falls back to the ARN attribute when the name identifier is Unassigned. See issue #5606.
+REFRESH_IDENTIFIER_FALLBACKS = {
+    "ModelPackage": {"ModelPackageName": "model_package_arn"},
+}
+
 
 class ResourcesCodeGen:
     """A class for generating resources based on a service JSON file.
@@ -761,7 +769,10 @@ def _generate_operation_input_args(
         return operation_input_args
 
     def _generate_operation_input_necessary_args(
-        self, resource_operation: dict, resource_attributes: list
+        self,
+        resource_operation: dict,
+        resource_attributes: list,
+        identifier_fallbacks: dict = None,
     ) -> str:
         """Generate the operation input arguments string.
 
@@ -770,7 +781,10 @@ def _generate_operation_input_necessary_args(
 
         Args:
             resource_operation (dict): The resource operation dictionary.
-            is_class_method (bool): Indicates method is class method, else object method.
+            resource_attributes (list): The resource object attributes available on self.
+            identifier_fallbacks (dict, optional): Maps an input member name to a resource
+                attribute to fall back to when the member's own attribute is Unassigned
+                (e.g. {"ModelPackageName": "model_package_arn"}). See issue #5606.
 
         Returns:
             str: The formatted operation input arguments string.
@@ -778,12 +792,22 @@ def _generate_operation_input_necessary_args(
         input_shape_name = resource_operation["input"]["shape"]
         input_shape_members = list(self.shapes[input_shape_name]["members"].keys())
 
+        identifier_fallbacks = identifier_fallbacks or {}
         args = list()
         for member in input_shape_members:
-            if convert_to_snake_case(member) in resource_attributes:
-                args.append(f"'{member}': self.{convert_to_snake_case(member)}")
+            snake_member = convert_to_snake_case(member)
+            if snake_member in resource_attributes:
+                if member in identifier_fallbacks:
+                    fallback_attr = identifier_fallbacks[member]
+                    args.append(
+                        f"'{member}': self.{snake_member} "
+                        f"if not isinstance(self.{snake_member}, Unassigned) "
+                        f"else self.{fallback_attr}"
+                    )
+                else:
+                    args.append(f"'{member}': self.{snake_member}")
             else:
-                args.append(f"'{member}': {convert_to_snake_case(member)}")
+                args.append(f"'{member}': {snake_member}")
 
         operation_input_args = ",\n".join(args)
         operation_input_args += ","
@@ -1300,7 +1324,9 @@ def generate_refresh_method(self, resource_name: str, **kwargs) -> str:
         )
 
         operation_input_args = self._generate_operation_input_necessary_args(
-            operation_metadata, kwargs["resource_attributes"]
+            operation_metadata,
+            kwargs["resource_attributes"],
+            identifier_fallbacks=REFRESH_IDENTIFIER_FALLBACKS.get(resource_name),
         )
 
         operation = convert_to_snake_case(operation_name)
diff --git a/sagemaker-core/tests/unit/generated/test_resources.py b/sagemaker-core/tests/unit/generated/test_resources.py
index 260408df19..d192443dec 100644
--- a/sagemaker-core/tests/unit/generated/test_resources.py
+++ b/sagemaker-core/tests/unit/generated/test_resources.py
@@ -935,3 +935,40 @@ def test_no_synthesis_without_output_data_config(self):
         )
 
         assert isinstance(job.model_artifacts, Unassigned)
+
+
+class TestModelPackageRefreshIdentifierFallback(unittest.TestCase):
+    """ModelPackage.refresh() must work for versioned packages (issue #5606).
+
+    ``ListModelPackages`` does not return ``ModelPackageName`` for versioned packages
+    inside a model package group, only ``ModelPackageArn``. Since ``DescribeModelPackage``
+    accepts either for the ``ModelPackageName`` parameter, refresh() falls back to the ARN
+    when the name is ``Unassigned``.
+    """
+
+    _ARN = "arn:aws:sagemaker:us-west-2:123456789012:model-package/my-group/1"
+
+    def _refresh_with(self, **attrs):
+        from sagemaker.core.resources import ModelPackage
+
+        pkg = ModelPackage.model_construct(**attrs)
+        with (
+            patch("sagemaker.core.resources.transform", return_value={}),
+            patch.object(Base, "get_sagemaker_client") as mock_get_client,
+        ):
+            client = mock_get_client.return_value
+            client.describe_model_package.return_value = {}
+            pkg.refresh()
+            return client
+
+    def test_refresh_falls_back_to_arn_when_name_unassigned(self):
+        from sagemaker.core.utils.utils import Unassigned
+
+        client = self._refresh_with(model_package_name=Unassigned(), model_package_arn=self._ARN)
+        client.describe_model_package.assert_called_once_with(ModelPackageName=self._ARN)
+
+    def test_refresh_uses_name_when_present(self):
+        client = self._refresh_with(
+            model_package_name="my-model-package", model_package_arn=self._ARN
+        )
+        client.describe_model_package.assert_called_once_with(ModelPackageName="my-model-package")