diff --git a/packages/common-library/src/common_library/basic_types.py b/packages/common-library/src/common_library/basic_types.py
index ab5278cd4f4..6964e6c4033 100644
--- a/packages/common-library/src/common_library/basic_types.py
+++ b/packages/common-library/src/common_library/basic_types.py
@@ -1,5 +1,12 @@
 from enum import StrEnum
 
+from pydantic_core import PydanticUndefined
+
+# SEE https://github.com/fastapi/fastapi/blob/master/fastapi/_compat.py#L75-L78
+#
+# Use as default when default_factory
+Undefined = PydanticUndefined
+
 
 class LogLevel(StrEnum):
     DEBUG = "DEBUG"
diff --git a/packages/models-library/src/models_library/_compat.py b/packages/models-library/src/models_library/_compat.py
deleted file mode 100644
index 1079ccef28a..00000000000
--- a/packages/models-library/src/models_library/_compat.py
+++ /dev/null
@@ -1,6 +0,0 @@
-from pydantic_core import PydanticUndefined
-
-# SEE https://github.com/fastapi/fastapi/blob/master/fastapi/_compat.py#L75-L78
-#
-# Use as default when default_factory
-Undefined = PydanticUndefined
diff --git a/packages/models-library/src/models_library/app_diagnostics.py b/packages/models-library/src/models_library/app_diagnostics.py
index 1f90bead808..fe0c77cbafb 100644
--- a/packages/models-library/src/models_library/app_diagnostics.py
+++ b/packages/models-library/src/models_library/app_diagnostics.py
@@ -1,9 +1,8 @@
 from typing import Annotated, Any
 
+from common_library.basic_types import Undefined
 from pydantic import AnyUrl, BaseModel, Field
 
-from ._compat import Undefined
-
 _Unset: Any = Undefined
 
 
diff --git a/packages/models-library/src/models_library/projects.py b/packages/models-library/src/models_library/projects.py
index 4776e84bce3..45db325b0da 100644
--- a/packages/models-library/src/models_library/projects.py
+++ b/packages/models-library/src/models_library/projects.py
@@ -7,12 +7,12 @@
 from typing import Annotated, Any, Final, TypeAlias
 from uuid import UUID
 
+from common_library.basic_types import Undefined
 from models_library.basic_types import ConstrainedStr
 from models_library.folders import FolderID
 from models_library.workspaces import WorkspaceID
 from pydantic import BaseModel, ConfigDict, Field, HttpUrl, field_validator
 
-from ._compat import Undefined
 from .basic_regex import DATE_RE, UUID_RE_BASE
 from .emails import LowerCaseEmailStr
 from .projects_access import AccessRights, GroupIDStr
diff --git a/packages/models-library/src/models_library/projects_nodes.py b/packages/models-library/src/models_library/projects_nodes.py
index 6ff1d8c1a4e..ebbc39045e4 100644
--- a/packages/models-library/src/models_library/projects_nodes.py
+++ b/packages/models-library/src/models_library/projects_nodes.py
@@ -5,6 +5,7 @@
 from copy import deepcopy
 from typing import Annotated, Any, TypeAlias, Union
 
+from common_library.basic_types import Undefined
 from pydantic import (
     BaseModel,
     ConfigDict,
@@ -18,7 +19,6 @@
     field_validator,
 )
 
-from ._compat import Undefined
 from .basic_types import EnvVarKey, KeyIDStr
 from .projects_access import AccessEnum
 from .projects_nodes_io import (
diff --git a/packages/service-integration/src/service_integration/osparc_config.py b/packages/service-integration/src/service_integration/osparc_config.py
index e5a69a87f95..f9e22e653cb 100644
--- a/packages/service-integration/src/service_integration/osparc_config.py
+++ b/packages/service-integration/src/service_integration/osparc_config.py
@@ -16,7 +16,7 @@
 from pathlib import Path
 from typing import Annotated, Any, Final, Literal
 
-from models_library._compat import Undefined
+from common_library.basic_types import Undefined
 from models_library.basic_types import SHA256Str
 from models_library.callbacks_mapping import CallbacksMapping
 from models_library.service_settings_labels import (
diff --git a/packages/settings-library/tests/test_base.py b/packages/settings-library/tests/test_base.py
index 879bf5868be..d4ebd987760 100644
--- a/packages/settings-library/tests/test_base.py
+++ b/packages/settings-library/tests/test_base.py
@@ -8,6 +8,7 @@
 from collections.abc import Callable
 from typing import Any
 
+import pydantic
 import pytest
 import settings_library.base
 from pydantic import BaseModel, ValidationError
@@ -23,6 +24,8 @@
 )
 from settings_library.email import SMTPSettings
 
+pydantic_version = ".".join(pydantic.__version__.split(".")[:2])
+
 S2 = json.dumps({"S_VALUE": 2})
 S3 = json.dumps({"S_VALUE": 3})
 
@@ -180,7 +183,7 @@ def test_create_settings_class_without_environ_fails(
         "loc": ("S_VALUE",),
         "msg": "Field required",
         "type": "missing",
-        "url": "https://errors.pydantic.dev/2.9/v/missing",
+        "url": f"https://errors.pydantic.dev/{pydantic_version}/v/missing",
     }
 
 
@@ -310,7 +313,7 @@ class SettingsClassExt(SettingsClass):
         "loc": ("INT_VALUE_TO_NOTHING",),
         "msg": "Input should be a valid integer, unable to parse string as an integer",
         "type": "int_parsing",
-        "url": "https://errors.pydantic.dev/2.9/v/int_parsing",
+        "url": f"https://errors.pydantic.dev/{pydantic_version}/v/int_parsing",
     }