Pydantic config keyword in TypeAdapter doesn't update the

The Fix

pip install pydantic==2.12.0

Based on closed pydantic/pydantic issue #9142 · 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

@@ -89,6 +89,10 @@ print(ta.validate_python([1, 2]))
 ```
 
+Configuration can't be provided if the type adapter directly wraps a type that support it, and a
+[usage error](../errors/usage_errors.md) is raised in this case.
+The [configuration propagation](#configuration-propagation) rules also apply.

repro.py

from pydantic import BaseModel, ConfigDict, TypeAdapter

data1 = [
    {
        "family": "fam",
        "order": "ord",
        "specie": "sp1",
        "ds1": "ds1",
    },
    {
        "family": "fam",
        "order": "ord",
        "specie": "sp2",
        "ds1": "ds1",
    },
    {
        "family": "fam",
        "order": "ord",
        "specie": "sp3",
        "ds1": "ds1",
    },
]

class Model1(BaseModel):
    family: str | None = None
    order: str | None = None
    specie: str | None = None
    ds1: str = Field(serialization_alias="category")

records = TypeAdapter(
    type=list[Model1],
    config=ConfigDict(extra="allow"),
).validate_python(data1)

print(records[0].model_extra) # -> None  // it should be {"extra": "allow"}

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==2.12.0\nWhen NOT to use: This fix is not applicable if the TypeAdapter wraps a type that already has its own configuration.\n\n

Why This Fix Works in Production

Trigger: from pydantic import BaseModel, ConfigDict, Field, TypeAdapter
Mechanism: The config keyword in TypeAdapter does not apply when the type is a BaseModel
Why the fix works: Clarifies TypeAdapter configuration rules in documentation, addressing the issue where the config keyword in TypeAdapter doesn't update the model. (first fixed release: 2.12.0).

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 3.11 in real deployments (not just unit tests).
The config keyword in TypeAdapter does not apply when the type is a BaseModel
Surfaces as: from pydantic import BaseModel, ConfigDict, Field, TypeAdapter

Proof / Evidence

GitHub issue: #9142
Fix PR: https://github.com/pydantic/pydantic/pull/12327
First fixed release: 2.12.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.43

Discussion

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

Jump to Sources Open on GitHub

“Hi, I see this is still open. Has this been resolved or not? If not I'd like to take on the documentation part mentioned by…”

@JonathanWindell · 2025-10-04 · confirmation · source

“@JonathanWindell thanks for volunteering. In https://docs.pydantic.dev/latest/concepts/config/#configuration-on-typeadapter, something along the lines of: can be added at the end of the section.”

@Viicos · 2025-10-04 · source

“This reminds me of: * https://github.com/pydantic/pydantic/pull/8364 * https://github.com/pydantic/pydantic/pull/8335”

@sydney-runkle · 2024-04-04 · source

“Hi all, thanks for your feedback here”

@sydney-runkle · 2024-04-02 · source

Failure Signature (Search String)

from pydantic import BaseModel, ConfigDict, Field, TypeAdapter

Error Message

Stack trace

error.txt

Error Message
-------------
from pydantic import BaseModel, ConfigDict, Field, TypeAdapter

data1 = {
    "family": "fam",
    "order": "ord",
    "specie": "sp1",
    "ds1": "ds1",
}

class Model1(BaseModel):
    family: str | None = None
    order: str | None = None
    specie: str | None = None
    ds1: str = Field(serialization_alias="category")

results = TypeAdapter(
    type=Model1,
    config=ConfigDict(extra="allow"),
).validate_python(data1)

print(results)
"""
pydantic.errors.PydanticUserError: Cannot use `config` when the type is a BaseModel, dataclass or TypedDict. 
These types can have their own config and setting the config via the `config` parameter to TypeAdapter will not override it, 
thus the `config` you passed to TypeAdapter becomes meaningless, which is probably not what you want.
"""

Minimal Reproduction

repro.py

from pydantic import BaseModel, ConfigDict, TypeAdapter

data1 = [
    {
        "family": "fam",
        "order": "ord",
        "specie": "sp1",
        "ds1": "ds1",
    },
    {
        "family": "fam",
        "order": "ord",
        "specie": "sp2",
        "ds1": "ds1",
    },
    {
        "family": "fam",
        "order": "ord",
        "specie": "sp3",
        "ds1": "ds1",
    },
]

class Model1(BaseModel):
    family: str | None = None
    order: str | None = None
    specie: str | None = None
    ds1: str = Field(serialization_alias="category")

records = TypeAdapter(
    type=list[Model1],
    config=ConfigDict(extra="allow"),
).validate_python(data1)

print(records[0].model_extra) # -> None  // it should be {"extra": "allow"}

Environment

Python: 3.11
Pydantic: 2

What Broke

Users experience unexpected behavior when using TypeAdapter with model configurations.

Why It Broke

The config keyword in TypeAdapter does not apply when the type is a BaseModel

Fix Options (Details)

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

pip install pydantic==2.12.0

When NOT to use: This fix is not applicable if the TypeAdapter wraps a type that already has its own configuration.

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/12327

First fixed release: 2.12.0

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

When NOT to Use This Fix

This fix is not applicable if the TypeAdapter wraps a type that already has its own configuration.

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.
Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Version Compatibility Table

Version	Status
2.12.0	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 config keyword in TypeAdapter doesn't update the model (Fix)