PydanticSerializationUnexpectedValue warning when using structured output for AzureChatOpenAI

[Natallia-Spichekova-vertex]

Checked other resources

• 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

PydanticSerializationUnexpectedValue warning when using structured output #35538

Reproduction Steps / Example Code (Python)

from langchain_openai import AzureChatOpenAI
from pydantic.main import BaseModel

gpt4_model = AzureChatOpenAI(...)

class ModelOutput(BaseModel):
    output: str

gpt4_model.with_structured_output(ModelOutput).invoke("What is the capital of France?")

Error Message and Stack Trace (if applicable)

PydanticSerializationUnexpectedValue(Expected `none` - serialized value may not be as expected [field_name='parsed', input_value=ModelOutput(output='The c...al of France is Paris.'), input_type=ModelOutput])
  return self.__pydantic_serializer__.to_python(

Description

Using structured output for AzureChatOpenAI produces a serializer warning.

System Info

System Information

OS: Linux
OS Version: #1 SMP PREEMPT_DYNAMIC Thu Jun 5 18:30:46 UTC 2025
Python Version: 3.12.3 (main, Mar 3 2026, 12:15:18) [GCC 13.3.0]

Package Information

langchain_core: 1.2.27
langsmith: 0.7.26
langchain_openai: 1.1.12

Optional packages not installed

deepagents
deepagents-cli

Other Dependencies

httpx: 0.28.1
jsonpatch: 1.33
openai: 2.30.0
orjson: 3.11.8
packaging: 26.0
pydantic: 2.12.5
pyyaml: 6.0.3
requests: 2.33.1
requests-toolbelt: 1.0.0
tenacity: 9.1.4
tiktoken: 0.12.0
typing-extensions: 4.15.0
uuid-utils: 0.14.1
xxhash: 3.6.0
zstandard: 0.25.0

[jasiecky]

Hey, I'd like to be assigned to this issue;) I've opened a PR.

ccurme (@ccurme) Mason Daugherty (@mdrxy)