Pydantic Deferred imports failure with Python 3.14 (Fix)

The Fix

pip install pydantic==2.12.4

Based on closed pydantic/pydantic issue #12421 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -526,6 +526,13 @@ def _eval_type(
             localns,
             type_params=type_params,
+            # This is relevant when evaluating types from `TypedDict` classes, where string annotations
+            # are automatically converted to `ForwardRef` instances with a module set. In this case,
+            # Our `globalns` is irrelevant and we need to indicate `typing._eval_type()` that it should

repro.py

from __future__ import annotations

from typing import TypedDict, Required

class A(TypedDict):
    x: Required[int]

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==2.12.4\nWhen NOT to use: This fix should not be used if the application relies on the previous behavior of deferred imports.\n\n

Why This Fix Works in Production

Trigger: python b.py
Mechanism: Fixes an issue with forward references in parent TypedDict classes that caused failures in Pydantic 2.12 when used with Python 3.14.
Why the fix works: Fixes an issue with forward references in parent TypedDict classes that caused failures in Pydantic 2.12 when used with Python 3.14. (first fixed release: 2.12.4).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

Shows up under Python 3.14 in real deployments (not just unit tests).
Surfaces as: python b.py

Proof / Evidence

GitHub issue: #12421
Fix PR: https://github.com/pydantic/pydantic/pull/12427
First fixed release: 2.12.4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.40

Discussion

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

Jump to Sources Open on GitHub

“### Initial Checks - [x] I confirm that I'm using Pydantic V2 ### Description Pydantic 2.12 fails to resolve deferred imports in Python 3.14 See the example below. Notes: * reproduced with Python 3.14.0 * not reproduced with Python 3.13.2 *”

Issue thread · issue description · source

Failure Signature (Search String)

python b.py

Error Message

Stack trace

error.txt

Error Message
-------------
python b.py
Traceback (most recent call last):
  File "/private/tmp/b.py", line 10, in <module>
    C.model_validate({"c": {"x": 1}})
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/christophe.bornet/.pyenv/versions/3.14.0/lib/python3.14/site-packages/pydantic/main.py", line 716, in model_validate
    return cls.__pydantic_validator__.validate_python(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/christophe.bornet/.pyenv/versions/3.14.0/lib/python3.14/site-packages/pydantic/_internal/_mock_val_ser.py", line 100, in __getattr__
    raise PydanticUserError(self._error_message, code=self._code)
pydantic.errors.PydanticUserError: `C` is not fully defined; you should define `Required`, then call `C.model_rebuild()`.

For further information visit https://errors.pydantic.dev/2.12/u/class-not-fully-defined

Minimal Reproduction

repro.py

from __future__ import annotations

from typing import TypedDict, Required

class A(TypedDict):
    x: Required[int]

Environment

Python: 3.14
Pydantic: 2

Fix Options (Details)

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

pip install pydantic==2.12.4

When NOT to use: This fix should not be used if the application relies on the previous behavior of deferred imports.

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/12427

First fixed release: 2.12.4

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

When NOT to Use This Fix

This fix should not be used if the application relies on the previous behavior of deferred imports.

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
2.12.4	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:data-consistency Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Configuration error OpenAPI schema Serialization

Sources

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