Pydantic Broken validation of fields in

The Fix

pip install pydantic==2.11.0

Based on closed pydantic/pydantic issue #11443 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -873,7 +873,7 @@ def _generate_schema_from_get_schema_method(self, obj: Any, source: Any) -> core
             return schema
 
-        if (validators := getattr(obj, '__get_validators__', None)) is not None:
+        if get_schema is None and (validators := getattr(obj, '__get_validators__', None)) is not None:
             from pydantic.v1 import BaseModel as BaseModelV1

repro.py

from pydantic import BaseModel

class Model(BaseModel):
    a: int
    @classmethod
    def __get_validators__(cls):
        yield cls._validate

    @classmethod
    def _validate(cls, value):
        raise ValueError

m = Model(a=1)  # runs fine.

class Other(BaseModel):
    m: Model

Other(m={'a': 1})
# ValueError

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install pydantic==2.11.0\nWhen NOT to use: This fix should not be applied if the model does not implement both methods correctly.\n\n

Why This Fix Works in Production

Trigger: m = MenuItem(command=a, when=None)
Mechanism: The validation method was incorrectly receiving an unexpected number of arguments
Why the fix works: Fixes the validation issue by not checking for `__get_validators__` on classes where `__get_pydantic_core_schema__` is also defined. (first fixed release: 2.11.0).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Shows up under Python 3.12 in real deployments (not just unit tests).
The validation method was incorrectly receiving an unexpected number of arguments
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #11443
Fix PR: https://github.com/pydantic/pydantic/pull/11444
First fixed release: 2.11.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.46

Verified Execution

We executed the runnable minimal repro in a temporary environment and captured exit codes + logs.

Status: PASS
Ran: 2026-02-11T16:52:29Z
Package: pydantic
Fixed: 2.11.0
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“right..”

@tlambert03 · 2025-02-14 · confirmation · source

“@Czaki, I think we should probably try to create a MRE here that leaves app-model and pydantic-compat out of it and only uses pydantic v2…”

@tlambert03 · 2025-02-14 · source

“Since Pydantic 2.3 the __get_validators__ is part of PyDantic 2. Until Tuesday, I will not have time to sit on MRE, and not sure what…”

@Czaki · 2025-02-14 · source

“Great to hear your are testing on the pre-releases. I'll investigate tomorrow.”

@Viicos · 2025-02-14 · source

Failure Signature (Search String)

m = MenuItem(command=a, when=None)

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/home/czaki/Projekty/app-model/tests/bug_reproduce.py", line 9, in <module>
    m = MenuItem(command=a, when=None)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/czaki/.pyenv/versions/app-model/lib/python3.12/site-packages/pydantic/main.py", line 230, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: MenuItemBase._validate() takes 2 positional arguments but 3 were given

Process finished with exit code 1

Minimal Reproduction

repro.py

from pydantic import BaseModel

class Model(BaseModel):
    a: int
    @classmethod
    def __get_validators__(cls):
        yield cls._validate

    @classmethod
    def _validate(cls, value):
        raise ValueError

m = Model(a=1)  # runs fine.

class Other(BaseModel):
    m: Model

Other(m={'a': 1})
# ValueError

Environment

Python: 3.12
Pydantic: 2

What Broke

CI jobs failed due to validation errors in Pydantic models.

Why It Broke

The validation method was incorrectly receiving an unexpected number of arguments

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install pydantic==2.11.0

When NOT to use: This fix should not be applied if the model does not implement both methods correctly.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pydantic/pydantic/pull/11444

First fixed release: 2.11.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the model does not implement both methods correctly.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
2.11.0	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:configuration-error Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Data consistency OpenAPI schema Serialization

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Pydantic Broken validation of fields in `pydantic==2.11.0a{1,2} (Fix)