diff --git a/src/browserbase/_base_client.py b/src/browserbase/_base_client.py
index 2bdf8f7..1955a7a 100644
--- a/src/browserbase/_base_client.py
+++ b/src/browserbase/_base_client.py
@@ -63,7 +63,7 @@
     ModelBuilderProtocol,
 )
 from ._utils import is_dict, is_list, asyncify, is_given, lru_cache, is_mapping
-from ._compat import model_copy, model_dump
+from ._compat import PYDANTIC_V2, model_copy, model_dump
 from ._models import GenericModel, FinalRequestOptions, validate_type, construct_type
 from ._response import (
     APIResponse,
@@ -207,6 +207,9 @@ def _set_private_attributes(
         model: Type[_T],
         options: FinalRequestOptions,
     ) -> None:
+        if PYDANTIC_V2 and getattr(self, "__pydantic_private__", None) is None:
+            self.__pydantic_private__ = {}
+
         self._model = model
         self._client = client
         self._options = options
@@ -292,6 +295,9 @@ def _set_private_attributes(
         client: AsyncAPIClient,
         options: FinalRequestOptions,
     ) -> None:
+        if PYDANTIC_V2 and getattr(self, "__pydantic_private__", None) is None:
+            self.__pydantic_private__ = {}
+
         self._model = model
         self._client = client
         self._options = options