`Failed to use model_dump to serialize <class 'langchain_core.tools.structured.StructuredTool'> to JSON: PydanticSerializationError(Unable to serialize unknown type: <class 'pydantic._internal._model_construction.ModelMetaclass'>)`

khteh · April 3, 2026, 5:09am

Saw this message in the log after upgrading the dependencies. What does it mean? Where is the source of the “Failure” and how to fix it?

keenborder786 · April 3, 2026, 11:30am

@khteh difficult to help you out, if you do not provide any sample code which raised this error.

khteh · April 3, 2026, 11:35am

That’s problem. I don’t know which line of code and whether it is my code which causes the issue. I can’t post a URL of my repository here.

keenborder786 · April 3, 2026, 12:50pm

@khteh can you then please share the langchain package versions of your environment by running the following command:
python -m langchain_core.sys_info

khteh · April 4, 2026, 2:16am

System Information
------------------
> OS:  Linux
> OS Version:  #20-Ubuntu SMP PREEMPT_DYNAMIC Fri Mar 13 20:07:29 UTC 2026
> Python Version:  3.13.7 (main, Mar  3 2026, 12:19:54) [GCC 15.2.0]

Package Information
-------------------
> langchain_core: 0.3.45
> langchain: 0.3.20
> langchain_community: 0.3.19
> langsmith: 0.3.15
> langchain_google_genai: 2.1.0
> langchain_google_vertexai: 2.0.15
> langchain_openai: 0.3.8
> langchain_text_splitters: 0.3.6
> langgraph_api: 0.2.38
> langgraph_cli: 0.2.10
> langgraph_license: Installed. No version info available.
> langgraph_runtime: Installed. No version info available.
> langgraph_runtime_inmem: 0.2.0
> langgraph_sdk: 0.1.70

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp<4.0.0,>=3.8.3: Installed. No version info available.
> anthropic[vertexai]: Installed. No version info available.
> async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
> blockbuster<2.0.0,>=1.5.24: Installed. No version info available.
> click: 8.1.8
> cloudpickle>=3.0.0: Installed. No version info available.
> cryptography<45.0,>=42.0.0: Installed. No version info available.
> dataclasses-json<0.7,>=0.5.7: Installed. No version info available.
> filetype: 1.2.0
> google-ai-generativelanguage: 0.6.16
> google-cloud-aiplatform: 1.84.0
> google-cloud-storage: 2.19.0
> httpx: 0.28.1
> httpx-sse: 0.4.0
> httpx-sse<1.0.0,>=0.4.0: Installed. No version info available.
> httpx>=0.25.0: Installed. No version info available.
> httpx>=0.25.2: Installed. No version info available.
> jsonpatch<2.0,>=1.33: Installed. No version info available.
> jsonschema-rs<0.30,>=0.20.0: Installed. No version info available.
> langchain-anthropic;: Installed. No version info available.
> langchain-aws;: Installed. No version info available.
> langchain-cohere;: Installed. No version info available.
> langchain-community;: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.34: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.41: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.42: Installed. No version info available.
> langchain-core>=0.2.38: Installed. No version info available.
> langchain-deepseek;: Installed. No version info available.
> langchain-fireworks;: Installed. No version info available.
> langchain-google-genai;: Installed. No version info available.
> langchain-google-vertexai;: Installed. No version info available.
> langchain-groq;: Installed. No version info available.
> langchain-huggingface;: Installed. No version info available.
> langchain-mistralai: Installed. No version info available.
> langchain-mistralai;: Installed. No version info available.
> langchain-ollama;: Installed. No version info available.
> langchain-openai;: Installed. No version info available.
> langchain-text-splitters<1.0.0,>=0.3.6: Installed. No version info available.
> langchain-together;: Installed. No version info available.
> langchain-xai;: Installed. No version info available.
> langchain<1.0.0,>=0.3.20: Installed. No version info available.
> langgraph-checkpoint>=2.0.23: Installed. No version info available.
> langgraph-checkpoint>=2.0.25: Installed. No version info available.
> langgraph-runtime-inmem<0.3,>=0.2.0: Installed. No version info available.
> langgraph-sdk>=0.1.66: Installed. No version info available.
> langgraph>=0.2: Installed. No version info available.
> langgraph>=0.3.27: Installed. No version info available.
> langsmith-pyo3: Installed. No version info available.
> langsmith<0.4,>=0.1.125: Installed. No version info available.
> langsmith<0.4,>=0.1.17: Installed. No version info available.
> langsmith>=0.1.112: Installed. No version info available.
> numpy<3,>=1.26.2: Installed. No version info available.
> openai-agents: Installed. No version info available.
> openai<2.0.0,>=1.58.1: Installed. No version info available.
> orjson: 3.10.15
> orjson>=3.10.1: Installed. No version info available.
> orjson>=3.9.7: Installed. No version info available.
> packaging: 24.2
> packaging<25,>=23.2: Installed. No version info available.
> pydantic: 2.10.6
> pydantic-settings<3.0.0,>=2.4.0: Installed. No version info available.
> pydantic<3.0.0,>=2.5.2;: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4;: Installed. No version info available.
> pyjwt>=2.9.0: Installed. No version info available.
> pytest: Installed. No version info available.
> python-dotenv: 1.0.1
> PyYAML>=5.3: Installed. No version info available.
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> requests<3,>=2: Installed. No version info available.
> rich: 13.9.4
> SQLAlchemy<3,>=1.4: Installed. No version info available.
> sse-starlette<2.2.0,>=2.1.0: Installed. No version info available.
> sse-starlette>=2: Installed. No version info available.
> starlette>=0.37: Installed. No version info available.
> starlette>=0.38.6: Installed. No version info available.
> structlog<26,>=24.1.0: Installed. No version info available.
> structlog>23: Installed. No version info available.
> tenacity!=8.4.0,<10,>=8.1.0: Installed. No version info available.
> tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
> tenacity>=8.0.0: Installed. No version info available.
> tiktoken<1,>=0.7: Installed. No version info available.
> truststore>=0.1: Installed. No version info available.
> typing-extensions>=4.7: Installed. No version info available.
> uvicorn>=0.26.0: Installed. No version info available.
> watchfiles>=0.13: Installed. No version info available.
> zstandard: 0.23.0

keenborder786 · April 4, 2026, 5:45am

Can you update langchain and langchain_core to latest versions and also update langsmith to latest version:

langchain → 1.2.15
langchain_core → 1.2.26
langsmith → 0.7.25

khteh · April 4, 2026, 11:59am

uv sync –upgrade doesn’t show any new package version to upgrade to.

khteh · April 4, 2026, 12:10pm

To no avail.

System Information
------------------
> OS:  Linux
> OS Version:  #20-Ubuntu SMP PREEMPT_DYNAMIC Fri Mar 13 20:07:29 UTC 2026
> Python Version:  3.13.7 (main, Mar  3 2026, 12:19:54) [GCC 15.2.0]

Package Information
-------------------
> langchain_core: 0.3.45
> langchain: 0.3.20
> langchain_community: 0.3.19
> langsmith: 0.3.15
> langchain_google_genai: 2.1.0
> langchain_google_vertexai: 2.0.15
> langchain_openai: 0.3.8
> langchain_text_splitters: 0.3.6
> langgraph_api: 0.2.38
> langgraph_cli: 0.2.10
> langgraph_license: Installed. No version info available.
> langgraph_runtime: Installed. No version info available.
> langgraph_runtime_inmem: 0.2.0
> langgraph_sdk: 0.1.70

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp<4.0.0,>=3.8.3: Installed. No version info available.
> anthropic[vertexai]: Installed. No version info available.
> async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
> blockbuster<2.0.0,>=1.5.24: Installed. No version info available.
> click: 8.1.8
> cloudpickle>=3.0.0: Installed. No version info available.
> cryptography<45.0,>=42.0.0: Installed. No version info available.
> dataclasses-json<0.7,>=0.5.7: Installed. No version info available.
> filetype: 1.2.0
> google-ai-generativelanguage: 0.6.16
> google-cloud-aiplatform: 1.84.0
> google-cloud-storage: 2.19.0
> httpx: 0.28.1
> httpx-sse: 0.4.0
> httpx-sse<1.0.0,>=0.4.0: Installed. No version info available.
> httpx>=0.25.0: Installed. No version info available.
> httpx>=0.25.2: Installed. No version info available.
> jsonpatch<2.0,>=1.33: Installed. No version info available.
> jsonschema-rs<0.30,>=0.20.0: Installed. No version info available.
> langchain-anthropic;: Installed. No version info available.
> langchain-aws;: Installed. No version info available.
> langchain-cohere;: Installed. No version info available.
> langchain-community;: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.34: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.41: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.42: Installed. No version info available.
> langchain-core>=0.2.38: Installed. No version info available.
> langchain-deepseek;: Installed. No version info available.
> langchain-fireworks;: Installed. No version info available.
> langchain-google-genai;: Installed. No version info available.
> langchain-google-vertexai;: Installed. No version info available.
> langchain-groq;: Installed. No version info available.
> langchain-huggingface;: Installed. No version info available.
> langchain-mistralai: Installed. No version info available.
> langchain-mistralai;: Installed. No version info available.
> langchain-ollama;: Installed. No version info available.
> langchain-openai;: Installed. No version info available.
> langchain-text-splitters<1.0.0,>=0.3.6: Installed. No version info available.
> langchain-together;: Installed. No version info available.
> langchain-xai;: Installed. No version info available.
> langchain<1.0.0,>=0.3.20: Installed. No version info available.
> langgraph-checkpoint>=2.0.23: Installed. No version info available.
> langgraph-checkpoint>=2.0.25: Installed. No version info available.
> langgraph-runtime-inmem<0.3,>=0.2.0: Installed. No version info available.
> langgraph-sdk>=0.1.66: Installed. No version info available.
> langgraph>=0.2: Installed. No version info available.
> langgraph>=0.3.27: Installed. No version info available.
> langsmith-pyo3: Installed. No version info available.
> langsmith<0.4,>=0.1.125: Installed. No version info available.
> langsmith<0.4,>=0.1.17: Installed. No version info available.
> langsmith>=0.1.112: Installed. No version info available.
> numpy<3,>=1.26.2: Installed. No version info available.
> openai-agents: Installed. No version info available.
> openai<2.0.0,>=1.58.1: Installed. No version info available.
> orjson: 3.10.15
> orjson>=3.10.1: Installed. No version info available.
> orjson>=3.9.7: Installed. No version info available.
> packaging: 24.2
> packaging<25,>=23.2: Installed. No version info available.
> pydantic: 2.10.6
> pydantic-settings<3.0.0,>=2.4.0: Installed. No version info available.
> pydantic<3.0.0,>=2.5.2;: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4;: Installed. No version info available.
> pyjwt>=2.9.0: Installed. No version info available.
> pytest: Installed. No version info available.
> python-dotenv: 1.0.1
> PyYAML>=5.3: Installed. No version info available.
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> requests<3,>=2: Installed. No version info available.
> rich: 13.9.4
> SQLAlchemy<3,>=1.4: Installed. No version info available.
> sse-starlette<2.2.0,>=2.1.0: Installed. No version info available.
> sse-starlette>=2: Installed. No version info available.
> starlette>=0.37: Installed. No version info available.
> starlette>=0.38.6: Installed. No version info available.
> structlog<26,>=24.1.0: Installed. No version info available.
> structlog>23: Installed. No version info available.
> tenacity!=8.4.0,<10,>=8.1.0: Installed. No version info available.
> tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
> tenacity>=8.0.0: Installed. No version info available.
> tiktoken<1,>=0.7: Installed. No version info available.
> truststore>=0.1: Installed. No version info available.
> typing-extensions>=4.7: Installed. No version info available.
> uvicorn>=0.26.0: Installed. No version info available.
> watchfiles>=0.13: Installed. No version info available.
> zstandard: 0.23.0

keenborder786 · April 5, 2026, 12:57pm

You need to update your pyproject.toml e.g "langchain>=1.2.15", this will ensure langchain is at a minimum of v1.2.15 and then run uv sync –upgrade so your environment get’s updated.

khteh · April 6, 2026, 4:42am

To no avail. I have upgraded to the latest langchain versions but the warning message still shows up.

System Information
------------------
> OS:  Linux
> OS Version:  #20-Ubuntu SMP PREEMPT_DYNAMIC Fri Mar 13 20:07:29 UTC 2026
> Python Version:  3.13.7 (main, Mar  3 2026, 12:19:54) [GCC 15.2.0]

Package Information
-------------------
> langchain_core: 1.2.26
> langchain: 1.2.15
> langchain_community: 0.4.1
> langsmith: 0.7.25
> deepagents: 0.4.12
> langchain_anthropic: 1.4.0
> langchain_classic: 1.0.3
> langchain_google_genai: 4.2.1
> langchain_neo4j: 0.9.0
> langchain_ollama: 1.0.1
> langchain_openai: 1.1.12
> langchain_postgres: 0.0.17
> langchain_text_splitters: 1.1.1
> langgraph_api: 0.7.27
> langgraph_cli: 0.4.19
> langgraph_runtime_inmem: 0.24.1
> langgraph_sdk: 0.3.12

Optional packages not installed
-------------------------------
> deepagents-cli

Other Dependencies
------------------
> aiohttp: 3.13.5
> anthropic: 0.89.0
> asyncpg: 0.31.0
> blockbuster: 1.5.26
> click: 8.3.2
> cloudpickle: 3.1.2
> croniter: 6.2.2
> cryptography: 46.0.6
> dataclasses-json: 0.6.7
> filetype: 1.2.0
> google-genai: 1.70.0
> grpcio: 1.80.0
> grpcio-health-checking: 1.80.0
> grpcio-tools: 1.75.1
> httpx: 0.28.1
> httpx-sse: 0.4.3
> jsonpatch: 1.33
> jsonschema-rs: 0.29.1
> langgraph: 1.1.6
> langgraph-checkpoint: 4.0.1
> neo4j: 6.1.0
> neo4j-graphrag: 1.14.1
> numpy: 2.4.4
> ollama: 0.6.1
> openai: 2.30.0
> opentelemetry-api: 1.40.0
> opentelemetry-exporter-otlp-proto-http: 1.40.0
> opentelemetry-sdk: 1.40.0
> orjson: 3.11.8
> packaging: 26.0
> pgvector: 0.3.6
> protobuf: 6.33.6
> psycopg: 3.3.3
> psycopg-pool: 3.3.0
> pydantic: 2.12.5
> pydantic-settings: 2.13.1
> pyjwt: 2.12.1
> pytest: 9.0.2
> python-dotenv: 1.2.2
> pyyaml: 6.0.3
> PyYAML: 6.0.3
> requests: 2.33.1
> requests-toolbelt: 1.0.0
> SQLAlchemy: 2.0.49
> sqlalchemy: 2.0.49
> sse-starlette: 2.1.3
> starlette: 1.0.0
> structlog: 25.5.0
> tenacity: 9.1.4
> tiktoken: 0.12.0
> truststore: 0.10.4
> typing-extensions: 4.15.0
> uuid-utils: 0.14.1
> uvicorn: 0.43.0
> watchfiles: 1.1.1
> wcmatch: 10.1
> websockets: 16.0
> xxhash: 3.6.0
> zstandard: 0.25.0

keenborder786 · April 6, 2026, 1:31pm

@kheth, thank you for trying it out. Could you now please post the stack trace of the error so I can see the exact place where it might be coming from?
Just copy and paste the stack trace from the CLI for this error.

keenborder786 · April 7, 2026, 8:57am

@kheth, in this thread we’re missing the original source of the warning. Could you point out where it originates in this case?

khteh · April 7, 2026, 11:08am

github.com/langchain-ai/langchain

`BaseTool.model_dump(mode="json")` fails on `args_schema`, `func`, and `coroutine` fields

opened 05:59AM - 04 Apr 26 UTC

khteh

core external

### Checked other resources - [x] This is a bug, not a usage question. - [x] I …added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] 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 - [x] 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) ```python from langchain_core.tools import StructuredTool from pydantic import BaseModel class Input(BaseModel): x: str def my_func(x: str) -> str: return x tool = StructuredTool.from_function(func=my_func, name="test", description="test", args_schema=Input) tool.model_dump(mode="json", exclude_none=True) # PydanticSerializationError(Unable to serialize unknown type: <class 'pydantic._internal._model_construction.ModelMetaclass'>) ``` ### Error Message and Stack Trace (if applicable) ```shell PydanticSerializationError(Unable to serialize unknown type: <class 'pydantic._internal._model_construction.ModelMetaclass'>) ``` ### Description `BaseTool.model_dump(mode="json")` raises `PydanticSerializationError` because three fields hold types that Pydantic cannot JSON-serialize: | Field | Holds | Problem | |---|---|---| | `args_schema` | A Pydantic model **class** (`type[BaseModel]`) | `ModelMetaclass` is not JSON-serializable | | `func` | A `Callable` | Functions are not JSON-serializable | | `coroutine` | A `Callable` | Functions are not JSON-serializable | This is not a functional bug — langsmith's tracing/serialization pipeline (`langsmith/_internal/_serde.py`) catches the exception and falls back to `str(obj)` — but the caught exception produces noisy `DEBUG`-level log messages on every tool serialization: ``` Failed to use model_dump to serialize <class 'langchain_core.tools.structured.StructuredTool'> to JSON: PydanticSerializationError(Unable to serialize unknown type: <class 'pydantic._internal._model_construction.ModelMetaclass'>) ``` **Proposed fix:** add `field_serializer` decorators to `BaseTool` for these three fields so that `model_dump(mode="json")` succeeds cleanly. For example: - `args_schema` → its JSON schema dict (via `model_json_schema()`) or the class name - `func` / `coroutine` → the function's qualified name string ### System Info Reproducible on all versions. Originally reported on `langchain_core==1.2.26`.

keenborder786 · April 7, 2026, 11:27am

Thank you for opening the issue. Hopefully the fix will be patched soon…

Topic		Replies	Views
`PydanticDeprecatedSince20: The `dict` method is deprecated; use `model_dump` instead. Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.12/migration/` LangSmith Product Help python-help	19	56	April 7, 2026
Parsing error with structured output with model output LangChain python-help	3	448	February 26, 2026
Feature (Code attached): Add JSON Schema Sanitizer for OpenAI Structured Outputs Compatibility Talking Shop	0	498	August 14, 2025
In langchain's ChatOpenai doc it's mentioned how to use structured output with tools, but what if I just wanna use strucutured output, how do I do it? LangSmith Product Help python-help	3	355	October 25, 2025
Tool call and structured ouput LangChain python-help	2	382	October 23, 2025

`Failed to use model_dump to serialize <class 'langchain_core.tools.structured.StructuredTool'> to JSON: PydanticSerializationError(Unable to serialize unknown type: <class 'pydantic._internal._model_construction.ModelMetaclass'>)`

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