diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index c16cffa1abf..be4c1ca19e7 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -2196,44 +2196,32 @@ def _resize(width: int, height: int) -> Tuple[int, int]:
 
 
 def _update_schema_with_optional_fields(input_dict: dict) -> dict:
-
+    """Convert optional fields to required fields allowing 'null' type."""
     def _update_properties(schema: dict):
-        if schema.get('type') != 'object':
+        if schema.get("type") != "object":
             return
 
-        properties = schema.get('properties', {})
-        required_fields = set(schema.get('required', []))
+        properties = schema.get("properties", {})
+        required_fields = schema.get("required", [])
 
         for field, field_schema in properties.items():
-            # Remove the 'default' key if it exists
-            field_schema.pop('default', None)
+            field_schema.pop("default", None)
 
-            if field_schema.get('type') == 'object':
+            if field_schema.get("type") == "object":
                 _update_properties(field_schema)
 
-            if 'allOf' in field_schema:
-                for sub_schema in field_schema['allOf']:
-                    if sub_schema.get('type') == 'object':
-                        _update_properties(sub_schema)
-
-            # if 'anyOf' in field_schema:
-            #     # Check if 'anyOf' contains a 'null' type
-            #     types = [sub_schema.get('type') for sub_schema in field_schema['anyOf']]
-            #     if 'null' not in types:
-            #         field_schema['anyOf'].append({'type': 'null'})
-
             if field not in required_fields:
-                original_type = field_schema.get('type')
+                original_type = field_schema.get("type")
                 if isinstance(original_type, str):
-                    field_schema['type'] = [original_type, 'null']
-                elif isinstance(original_type, list) and 'null' not in original_type:
-                    field_schema['type'].append('null')
+                    field_schema["type"] = [original_type, "null"]
+                elif isinstance(original_type, list) and "null" not in original_type:
+                    field_schema["type"].append("null")
 
-                required_fields.add(field)
+                required_fields.append(field)
 
-        schema['required'] = list(required_fields)
+        schema["required"] = required_fields
 
-    schema = input_dict.get('json_schema', {}).get('schema', {})
+    schema = input_dict.get("json_schema", {}).get("schema", {})
     _update_properties(schema)
 
     return input_dict
diff --git a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
index 2e6cca0cd2d..d588cc82dd8 100644
--- a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
+++ b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
@@ -18,7 +18,7 @@ from langchain_core.messages import (
 )
 from langchain_core.messages.ai import UsageMetadata
 from pydantic import BaseModel, Field
-from typing_extensions import TypedDict
+from typing_extensions import Annotated, TypedDict
 
 from langchain_openai import ChatOpenAI
 from langchain_openai.chat_models.base import (
@@ -822,6 +822,69 @@ def test__convert_to_openai_response_format() -> None:
     with pytest.raises(ValueError):
         _convert_to_openai_response_format(response_format, strict=False)
 
+    # Test handling of optional fields
+    ## TypedDict
+    class Entity(TypedDict):
+        """Extracted entity."""
+
+        animal: Annotated[str, ..., "The animal"]
+        color: Annotated[Optional[str], None, "The color"]
+
+    actual = _convert_to_openai_response_format(Entity, strict=True)
+    expected = {
+        "type": "json_schema",
+        "json_schema": {
+            "name": "Entity",
+            "description": "Extracted entity.",
+            "strict": True,
+            "schema": {
+                "type": "object",
+                "properties": {
+                    "animal": {"description": "The animal", "type": "string"},
+                    "color": {"description": "The color", "type": ["string", "null"]},
+                },
+                "required": ["animal", "color"],
+                "additionalProperties": False,
+            },
+        },
+    }
+    assert expected == actual
+
+    ## JSON Schema
+    class Entity(BaseModel):
+        """Extracted entity."""
+
+        animal: str = Field(description="The animal")
+        color: Optional[str] = Field(default=None, description="The color")
+
+    actual = _convert_to_openai_response_format(Entity.model_json_schema(), strict=True)
+    expected = {
+        "type": "json_schema",
+        "json_schema": {
+            "name": "Entity",
+            "description": "Extracted entity.",
+            "strict": True,
+            "schema": {
+                "properties": {
+                    "animal": {
+                        "description": "The animal",
+                        "title": "Animal",
+                        "type": "string",
+                    },
+                    "color": {
+                        "anyOf": [{"type": "string"}, {"type": "null"}],
+                        "description": "The color",
+                        "title": "Color",
+                    },
+                },
+                "required": ["animal", "color"],
+                "type": "object",
+                "additionalProperties": False,
+            },
+        },
+    }
+    assert expected == actual
+
 
 @pytest.mark.parametrize("method", ["function_calling", "json_schema"])
 @pytest.mark.parametrize("strict", [True, None])