@@ -3141,13 +3141,16 @@ def _create_sagemaker_model(self):
             sagemaker_session=self.sagemaker_session,
         )
 
-        # Nova 1P images require network isolation on the Model resource
+        # Nova 1P images require network isolation on the Model resource.
+        # A pipeline-variable image is only resolved at execution time, so it
+        # cannot be inspected here; set enable_network_isolation explicitly then.
         enable_network_isolation = self._enable_network_isolation
         resolved_image_uri = (
             container_def["Image"] if isinstance(container_def, dict) else container_def[0]["Image"]
         )
         if (
             not enable_network_isolation
+            and isinstance(resolved_image_uri, str)
             and "nova-" in resolved_image_uri
             and is_1p_image_uri(resolved_image_uri)
         ):
 
@@ -4,6 +4,9 @@
 
 import logging
 import re
+from typing import Optional
+
+from sagemaker.core.helper.pipeline_variable import StrPipeVar
 
 logger = logging.getLogger(__name__)
 
@@ -318,8 +321,15 @@
 }
 
 
-def is_1p_image_uri(image_uri: str) -> bool:
-    """Shows if the given image_uri is owned by a 1st party account"""
+def is_1p_image_uri(image_uri: Optional[StrPipeVar]) -> bool:
+    """Shows if the given image_uri is owned by a 1st party account.
+
+    A pipeline variable (e.g. ``ParameterString``) is only resolved at pipeline
+    execution time, so its account cannot be inspected at build time. Such values,
+    and any other non-string value, are treated as not 1st party.
+    """
+    if not isinstance(image_uri, str):
+        return False
     image_uri_account = image_uri[0:12]
     return image_uri_account in all_accounts
 
 
@@ -0,0 +1,124 @@
+"""Unit tests for ModelBuilder with a pipeline-variable image_uri (issue #5760)."""
+
+import unittest
+from unittest.mock import Mock, patch
+
+import boto3
+
+from sagemaker.core.workflow.parameters import ParameterString
+from sagemaker.core.workflow.pipeline_context import PipelineSession, _ModelStepArguments
+from sagemaker.serve.model_builder import ModelBuilder
+
+ROLE_ARN = "arn:aws:iam::123456789012:role/TestRole"
+TELEMETRY_MODULE = "sagemaker.core.telemetry.telemetry_logging"
+NOVA_1P_IMAGE = "708977205387.dkr.ecr.us-east-1.amazonaws.com/nova-inference:latest"
+
+
+def _mock_session():
+    session = Mock()
+    session.boto_region_name = "us-west-2"
+    session.default_bucket.return_value = "test-bucket"
+    session.default_bucket_prefix = None
+    session.config = {}
+    session.sagemaker_config = {}
+    return session
+
+
+class TestBuildValidationsWithPipelineVariableImageUri(unittest.TestCase):
+    """_build_validations must not slice a pipeline-variable image_uri."""
+
+    def test_image_only_pipeline_variable_is_passthrough(self):
+        builder = ModelBuilder(
+            image_uri=ParameterString(name="ServingImageUri"),
+            role_arn=ROLE_ARN,
+            sagemaker_session=_mock_session(),
+        )
+
+        builder._build_validations()
+
+        self.assertTrue(builder._passthrough)
+
+    def test_pipeline_variable_with_model_requires_model_server(self):
+        builder = ModelBuilder(
+            model=Mock(),
+            image_uri=ParameterString(name="ServingImageUri"),
+            role_arn=ROLE_ARN,
+            sagemaker_session=_mock_session(),
+        )
+
+        with self.assertRaises(ValueError) as context:
+            builder._build_validations()
+
+        self.assertIn("Model_server must be set", str(context.exception))
+
+
+@patch("sagemaker.serve.model_builder.resolve_nested_dict_value_from_config")
+@patch("sagemaker.serve.model_builder.resolve_value_from_config")
+@patch.object(ModelBuilder, "_init_sagemaker_session_if_does_not_exist")
+@patch.object(ModelBuilder, "_prepare_container_def")
+class TestCreateSageMakerModelNetworkIsolation(unittest.TestCase):
+    """The Nova network-isolation check must tolerate a pipeline-variable image."""
+
+    def _run(self, image_uri, mock_prepare, mock_resolve, mock_resolve_nested):
+        mock_prepare.return_value = {"Image": image_uri, "Environment": {}}
+        mock_resolve.side_effect = lambda value, *args, **kwargs: value
+        mock_resolve_nested.side_effect = lambda value, *args, **kwargs: value
+
+        session = Mock(spec=PipelineSession)
+        builder = ModelBuilder(
+            image_uri=image_uri,
+            role_arn=ROLE_ARN,
+            sagemaker_session=_mock_session(),
+        )
+        builder.sagemaker_session = session
+        builder.model_name = "test-model"
+
+        builder._create_sagemaker_model()
+
+        session.create_model.assert_called_once()
+        return session.create_model.call_args.kwargs
+
+    def test_pipeline_variable_image_does_not_raise(
+        self, mock_prepare, mock_init, mock_resolve, mock_resolve_nested
+    ):
+        image_uri = ParameterString(name="ServingImageUri")
+
+        kwargs = self._run(image_uri, mock_prepare, mock_resolve, mock_resolve_nested)
+
+        self.assertIs(kwargs["container_defs"]["Image"], image_uri)
+        self.assertFalse(kwargs["enable_network_isolation"])
+
+    def test_nova_1p_string_image_still_enables_network_isolation(
+        self, mock_prepare, mock_init, mock_resolve, mock_resolve_nested
+    ):
+        kwargs = self._run(NOVA_1P_IMAGE, mock_prepare, mock_resolve, mock_resolve_nested)
+
+        self.assertTrue(kwargs["enable_network_isolation"])
+
+
+@patch(f"{TELEMETRY_MODULE}.resolve_value_from_config", return_value=False)
+@patch(f"{TELEMETRY_MODULE}._send_telemetry_request")
+@patch("sagemaker.serve.model_builder.resolve_and_validate_role", return_value=ROLE_ARN)
+@patch.object(PipelineSession, "default_bucket", return_value="test-bucket")
+class TestBuildWithPipelineVariableImageUri(unittest.TestCase):
+    """End-to-end build() under a PipelineSession, as reported in #5760."""
+
+    def test_build_keeps_pipeline_variable_in_create_model_request(self, *_mocks):
+        image_uri = ParameterString(name="ServingImageUri")
+        session = PipelineSession(
+            boto_session=boto3.Session(
+                region_name="us-west-2",
+                aws_access_key_id="testing",
+                aws_secret_access_key="testing",
+            )
+        )
+        builder = ModelBuilder(image_uri=image_uri, role_arn=ROLE_ARN, sagemaker_session=session)
+
+        step_args = builder.build()
+
+        self.assertIsInstance(step_args, _ModelStepArguments)
+        self.assertIs(step_args.create_model_request["PrimaryContainer"]["Image"], image_uri)
+
+
+if __name__ == "__main__":
+    unittest.main()
@@ -1,4 +1,6 @@
 import unittest
+from sagemaker.core.workflow.functions import Join
+from sagemaker.core.workflow.parameters import ParameterString
 from sagemaker.serve.validations.check_image_uri import (
     is_1p_image_uri,
     all_accounts,
@@ -73,6 +75,23 @@ def test_all_accounts_contains_known_accounts(self):
         self.assertIn("763104351884", all_accounts)
         self.assertIn("246618743249", all_accounts)
 
+    def test_is_1p_image_uri_pipeline_variable_returns_false(self):
+        # A pipeline variable is only resolved at execution time, so it must not be
+        # sliced (TypeError, #5760); it is treated as not 1P, even if its default
+        # value would be a 1P image.
+        image_uri = ParameterString(
+            name="ServingImageUri",
+            default_value="763104351884.dkr.ecr.us-east-1.amazonaws.com/pytorch:latest",
+        )
+        self.assertFalse(is_1p_image_uri(image_uri))
+
+    def test_is_1p_image_uri_pipeline_function_returns_false(self):
+        image_uri = Join(on="", values=["763104351884", ParameterString(name="Suffix")])
+        self.assertFalse(is_1p_image_uri(image_uri))
+
+    def test_is_1p_image_uri_none_returns_false(self):
+        self.assertFalse(is_1p_image_uri(None))
+
 
 if __name__ == "__main__":
     unittest.main()