diff --git a/src/agent.py b/src/agent.py
index b146afae1..c8daf41da 100644
--- a/src/agent.py
+++ b/src/agent.py
@@ -175,8 +175,16 @@ async def async_response_stream(
             try:
                 # Try to serialize the chunk object
                 if hasattr(chunk, "model_dump"):
-                    # Pydantic model
-                    chunk_data = chunk.model_dump()
+                    # Pydantic model. Exclude "delta" from serialization since Langflow's
+                    # /response SSE wraps text deltas as {"content": "..."} for every provider but
+                    # openai SDK's event models declare/expect delta to be str so model_dump() will
+                    # emit noisy logs (PydanticSerializationUnexpectedValue) for every chunk. Basically
+                    # just reattach the raw (unvalidated) value afterwards to preserve same shape.
+                    # TODO: replace this with just chunk.model_dump() if langflow's /response SSE matches openai's
+                    # SDK's delta: str schema
+                    chunk_data = chunk.model_dump(exclude={"delta"})
+                    if hasattr(chunk, "delta"):
+                        chunk_data["delta"] = chunk.delta
                 elif hasattr(chunk, "__dict__"):
                     chunk_data = chunk.__dict__
                 else:
diff --git a/tests/unit/test_agent_stream_delta.py b/tests/unit/test_agent_stream_delta.py
new file mode 100644
index 000000000..c6f59681f
--- /dev/null
+++ b/tests/unit/test_agent_stream_delta.py
@@ -0,0 +1,38 @@
+import warnings
+
+from pydantic import BaseModel
+
+
+class FakeTextDeltaEvent(BaseModel):
+    """Mirrors openai's ResponseTextDeltaEvent: `delta` is declared as `str`."""
+
+    delta: str
+    type: str
+
+
+chunk = FakeTextDeltaEvent.model_construct(
+    delta={"content": "Hello"}, type="response.output_text.delta"
+)
+
+
+def test_model_dump_without_exclusion_raises_serialization_warning() -> None:
+    with warnings.catch_warnings(record=True) as recorded:
+        warnings.simplefilter("always")
+        chunk.model_dump()
+
+    assert any(
+        issubclass(w.category, UserWarning)
+        and "PydanticSerializationUnexpectedValue" in str(w.message)
+        for w in recorded
+    ), "expected a PydanticSerializationUnexpectedValue warning for the delta type mismatch"
+
+
+def test_model_dump_excluding_delta_avoids_warning_and_preserves_dict_shape() -> None:
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
+
+        chunk_data = chunk.model_dump(exclude={"delta"})
+        chunk_data["delta"] = chunk.delta
+
+    assert chunk_data["delta"] == {"content": "Hello"}
+    assert chunk_data["type"] == "response.output_text.delta"