langchain - 💡(How to fix) Fix UserWarning: Pydantic serializer warnings:

Submission checklist

• This is a bug, not a usage question.
• I added a clear and descriptive title that summarizes this issue.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
• This is not related to the langchain-community package.
• I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS.

Package (Required)

• langchain
• langchain-openai
• langchain-anthropic
• langchain-classic
• langchain-core
• langchain-model-profiles
• langchain-tests
• langchain-text-splitters
• langchain-chroma
• langchain-deepseek
• langchain-exa
• langchain-fireworks
• langchain-groq
• langchain-huggingface
• langchain-mistralai
• langchain-nomic
• langchain-ollama
• langchain-openrouter
• langchain-perplexity
• langchain-qdrant
• langchain-xai
• Other / not sure / general

Related Issues / PRs

No response

Reproduction Steps / Example Code (Python)

intent_recognition_output = (
            get_llm()
            .with_structured_output(IntentRecognitionOutput, include_raw=False)
            .invoke([
                SystemMessage(content=sys_prompt)
            ])
        )

class IntentRecognitionOutput(BaseModel):
    classification: str

    model_config = ConfigDict(
        extra="ignore"
    )

from typing import Optional

from langchain_openai import ChatOpenAI

from app.config import settings
from app.infra.logger.logger import log

_llm: ChatOpenAI | None = None


def get_llm() -> ChatOpenAI:
    """
    Get the ChatOpenAI LLM instance.

    Returns:
        BaseChatModel: Configured LLM instance
    """
    global _llm

    if _llm is None:
        _llm = ChatOpenAI(
            model=settings.LLM_MODEL,
            base_url=settings.LLM_BASE_URL,
            api_key=settings.LLM_API_KEY,
        )

    return _llm

Error Message and Stack Trace (if applicable)

Description

UserWarning: Pydantic serializer warnings: PydanticSerializationUnexpectedValue(Expected none - serialized value may not be as expected [field_name='parsed', input_value=IntentRecognitionOutput(c...xxxx》'), input_type=IntentRecognitionOutput]) return self.pydantic_serializer.to_python(

System Info

System Information

OS: Darwin OS Version: Darwin Kernel Version 25.5.0: Mon Apr 27 20:41:26 PDT 2026; root:xnu-12377.121.6~2/RELEASE_ARM64_T8132 Python Version: 3.12.13 (main, Apr 7 2026, 21:09:58) [Clang 22.1.1 ]

Package Information

langchain_core: 1.4.0 langchain: 1.3.2 langchain_community: 0.4.2 langsmith: 0.8.5 langchain_classic: 1.0.7 langchain_docling: 2.0.0 langchain_milvus: 0.3.3 langchain_openai: 1.2.2 langchain_protocol: 0.0.15 langchain_text_splitters: 1.1.2 langchain_unstructured: 1.0.1 langgraph_sdk: 0.3.15

Optional packages not installed

deepagents deepagents-cli

Other Dependencies

aiohttp: 3.13.5 docling: 2.95.0 httpx: 0.28.1 httpx-sse: 0.4.3 jsonpatch: 1.33 langgraph: 1.2.2 numpy: 2.3.5 openai: 2.38.0 opentelemetry-api: 1.42.1 opentelemetry-exporter-otlp-proto-http: 1.42.1 opentelemetry-sdk: 1.42.1 orjson: 3.11.9 packaging: 26.2 pydantic: 2.13.4 pydantic-settings: 2.14.1 pymilvus: 2.6.14 pytest: 9.0.3 pyyaml: 6.0.2 requests: 2.34.2 requests-toolbelt: 1.0.0 rich: 15.0.0 sqlalchemy: 2.0.50 tenacity: 9.1.4 tiktoken: 0.13.0 typing-extensions: 4.15.0 unstructured: 0.21.5 unstructured-client: 0.44.0 uuid-utils: 0.16.0 websockets: 16.0 wrapt: 1.17.3 xxhash: 3.7.0 zstandard: 0.25.0