diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 529006a8d5..9e6e24e53d 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "1.109.0"
+  ".": "1.109.1"
 }
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15e8f62701..24aced9a9d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 1.109.1 (2025-09-24)
+
+Full Changelog: [v1.109.0...v1.109.1](https://github.com/openai/openai-python/compare/v1.109.0...v1.109.1)
+
+### Bug Fixes
+
+* **compat:** compat with `pydantic<2.8.0` when using additional fields ([5d95ecf](https://github.com/openai/openai-python/commit/5d95ecf7abd65f3e4e273be14c80f9b4cd91ffe8))
+
 ## 1.109.0 (2025-09-23)
 
 Full Changelog: [v1.108.2...v1.109.0](https://github.com/openai/openai-python/compare/v1.108.2...v1.109.0)
diff --git a/pyproject.toml b/pyproject.toml
index 26dfbcf443..b89b4e25bd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "openai"
-version = "1.109.0"
+version = "1.109.1"
 description = "The official Python library for the openai API"
 dynamic = ["readme"]
 license = "Apache-2.0"
diff --git a/src/openai/_version.py b/src/openai/_version.py
index 16f48fb404..53c9794d8f 100644
--- a/src/openai/_version.py
+++ b/src/openai/_version.py
@@ -1,4 +1,4 @@
 # File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
 
 __title__ = "openai"
-__version__ = "1.109.0"  # x-release-please-version
+__version__ = "1.109.1"  # x-release-please-version
diff --git a/src/openai/types/evals/runs/output_item_list_response.py b/src/openai/types/evals/runs/output_item_list_response.py
index f774518f3c..e88c21766f 100644
--- a/src/openai/types/evals/runs/output_item_list_response.py
+++ b/src/openai/types/evals/runs/output_item_list_response.py
@@ -27,12 +27,17 @@ class Result(BaseModel):
     type: Optional[str] = None
     """The grader type (for example, "string-check-grader")."""
 
-    __pydantic_extra__: Dict[str, object] = FieldInfo(init=False)  # pyright: ignore[reportIncompatibleVariableOverride]
     if TYPE_CHECKING:
+        # Some versions of Pydantic <2.8.0 have a bug and don’t allow assigning a
+        # value to this field, so for compatibility we avoid doing it at runtime.
+        __pydantic_extra__: Dict[str, object] = FieldInfo(init=False)  # pyright: ignore[reportIncompatibleVariableOverride]
+
         # Stub to indicate that arbitrary properties are accepted.
         # To access properties that are not valid identifiers you can use `getattr`, e.g.
         # `getattr(obj, '$type')`
         def __getattr__(self, attr: str) -> object: ...
+    else:
+        __pydantic_extra__: Dict[str, object]
 
 
 class SampleInput(BaseModel):
diff --git a/src/openai/types/evals/runs/output_item_retrieve_response.py b/src/openai/types/evals/runs/output_item_retrieve_response.py
index d66435bd4f..c728629b41 100644
--- a/src/openai/types/evals/runs/output_item_retrieve_response.py
+++ b/src/openai/types/evals/runs/output_item_retrieve_response.py
@@ -27,12 +27,17 @@ class Result(BaseModel):
     type: Optional[str] = None
     """The grader type (for example, "string-check-grader")."""
 
-    __pydantic_extra__: Dict[str, object] = FieldInfo(init=False)  # pyright: ignore[reportIncompatibleVariableOverride]
     if TYPE_CHECKING:
+        # Some versions of Pydantic <2.8.0 have a bug and don’t allow assigning a
+        # value to this field, so for compatibility we avoid doing it at runtime.
+        __pydantic_extra__: Dict[str, object] = FieldInfo(init=False)  # pyright: ignore[reportIncompatibleVariableOverride]
+
         # Stub to indicate that arbitrary properties are accepted.
         # To access properties that are not valid identifiers you can use `getattr`, e.g.
         # `getattr(obj, '$type')`
         def __getattr__(self, attr: str) -> object: ...
+    else:
+        __pydantic_extra__: Dict[str, object]
 
 
 class SampleInput(BaseModel):