diff --git a/src/openai/types/responses/parsed_response.py b/src/openai/types/responses/parsed_response.py
index a859710590..5a27488e3d 100644
--- a/src/openai/types/responses/parsed_response.py
+++ b/src/openai/types/responses/parsed_response.py
@@ -3,6 +3,11 @@
 from typing import TYPE_CHECKING, List, Union, Generic, TypeVar, Optional
 from typing_extensions import Annotated, TypeAlias
 
+from ..._compat import PYDANTIC_V1
+
+if not PYDANTIC_V1:
+    from pydantic import SerializeAsAny
+
 from ..._utils import PropertyInfo
 from .response import Response
 from ..._models import GenericModel
@@ -53,8 +58,10 @@ class ParsedResponseOutputText(ResponseOutputText, GenericModel, Generic[Content
 class ParsedResponseOutputMessage(ResponseOutputMessage, GenericModel, Generic[ContentType]):
     if TYPE_CHECKING:
         content: List[ParsedContent[ContentType]]  # type: ignore[assignment]
+    elif not PYDANTIC_V1:
+        content: List[SerializeAsAny[ParsedContent]]
     else:
-        content: List[ParsedContent]
+        content: List[ParsedContent]  # type: ignore[assignment]
 
 
 class ParsedResponseFunctionToolCall(ResponseFunctionToolCall):
@@ -92,8 +99,10 @@ class ParsedResponseFunctionToolCall(ResponseFunctionToolCall):
 class ParsedResponse(Response, GenericModel, Generic[ContentType]):
     if TYPE_CHECKING:
         output: List[ParsedResponseOutputItem[ContentType]]  # type: ignore[assignment]
+    elif not PYDANTIC_V1:
+        output: List[SerializeAsAny[ParsedResponseOutputItem]]
     else:
-        output: List[ParsedResponseOutputItem]
+        output: List[ParsedResponseOutputItem]  # type: ignore[assignment]
 
     @property
     def output_parsed(self) -> Optional[ContentType]:
diff --git a/tests/lib/responses/test_parsed_response_serialization.py b/tests/lib/responses/test_parsed_response_serialization.py
new file mode 100644
index 0000000000..095e81cc1b
--- /dev/null
+++ b/tests/lib/responses/test_parsed_response_serialization.py
@@ -0,0 +1,109 @@
+"""Regression tests for PydanticSerializationUnexpectedValue warnings.
+
+See https://github.com/openai/openai-python/issues/2872
+"""
+from __future__ import annotations
+
+import warnings
+
+from pydantic import BaseModel
+
+from openai._models import construct_type_unchecked
+from openai.types.responses import Response
+from openai.lib._parsing._responses import parse_response
+
+
+class GuardrailDecision(BaseModel):
+    triggered: bool
+    reason: str
+
+
+def _make_raw_response() -> Response:
+    """Build a minimal Response object from a dict — no API call needed."""
+    return construct_type_unchecked(
+        type_=Response,
+        value={
+            "id": "resp_test123",
+            "object": "response",
+            "created_at": 1234567890.0,
+            "model": "gpt-4o-mini",
+            "output": [
+                {
+                    "id": "msg_test123",
+                    "type": "message",
+                    "status": "completed",
+                    "role": "assistant",
+                    "content": [
+                        {
+                            "type": "output_text",
+                            "text": '{"triggered": true, "reason": "test content flagged"}',
+                            "annotations": [],
+                        }
+                    ],
+                }
+            ],
+            "parallel_tool_calls": True,
+            "tool_choice": "auto",
+            "tools": [],
+            "temperature": 1.0,
+            "top_p": 1.0,
+            "text": {"format": {"type": "text"}},
+            "truncation": "disabled",
+        },
+    )
+
+
+def test_parsed_response_model_dump_no_warnings() -> None:
+    """model_dump() should not emit PydanticSerializationUnexpectedValue warnings."""
+    raw = _make_raw_response()
+    parsed = parse_response(
+        text_format=GuardrailDecision, input_tools=None, response=raw
+    )
+
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        data = parsed.model_dump()
+        pydantic_warnings = [
+            x for x in w if "PydanticSerializationUnexpectedValue" in str(x.message)
+        ]
+
+    assert len(pydantic_warnings) == 0, (
+        f"Expected 0 PydanticSerializationUnexpectedValue warnings, "
+        f"got {len(pydantic_warnings)}: {[str(x.message) for x in pydantic_warnings]}"
+    )
+
+    # Verify the parsed data is preserved correctly
+    assert data["output"][0]["content"][0]["parsed"] == {
+        "triggered": True,
+        "reason": "test content flagged",
+    }
+
+
+def test_parsed_response_model_dump_json_no_warnings() -> None:
+    """model_dump_json() should not emit PydanticSerializationUnexpectedValue warnings."""
+    raw = _make_raw_response()
+    parsed = parse_response(
+        text_format=GuardrailDecision, input_tools=None, response=raw
+    )
+
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        parsed.model_dump_json()
+        pydantic_warnings = [
+            x for x in w if "PydanticSerializationUnexpectedValue" in str(x.message)
+        ]
+
+    assert len(pydantic_warnings) == 0
+
+
+def test_parsed_response_output_parsed() -> None:
+    """output_parsed property should return the parsed object."""
+    raw = _make_raw_response()
+    parsed = parse_response(
+        text_format=GuardrailDecision, input_tools=None, response=raw
+    )
+
+    result = parsed.output_parsed
+    assert isinstance(result, GuardrailDecision)
+    assert result.triggered is True
+    assert result.reason == "test content flagged"