Pydantic `from __future__ import annotations` causes

The Fix

pip install pydantic==2.6.0

Based on closed pydantic/pydantic issue #8752 · 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

@@ -538,16 +538,23 @@ def _model_schema(self, cls: type[BaseModel]) -> core_schema.CoreSchema:
             extras_schema = None
             if core_config.get('extra_fields_behavior') == 'allow':
-                for tp in (cls, *cls.__mro__):
-                    extras_annotation = cls.__annotations__.get('__pydantic_extra__', None)
+                assert cls.__mro__[0] is cls

repro.py

from __future__ import annotations  # <- removing this line solves the problem

from pydantic import BaseModel, ConfigDict


class Test(BaseModel):
    model_config = ConfigDict(extra='allow')
    __pydantic_extra__: dict[str, str]

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==2.6.0\nWhen NOT to use: Do not use this fix if your model does not include `__pydantic_extra__`.\n\n

Why This Fix Works in Production

Trigger: class Test(BaseModel):
Mechanism: The type annotation for `__pydantic_extra__` was incorrectly defined, causing schema generation errors
Why the fix works: Handles the `__pydantic_extra__` annotation being a string or inherited, fixing the type annotation error caused by `from __future__ import annotations`. (first fixed release: 2.6.0).

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 3.10 in real deployments (not just unit tests).
The type annotation for `__pydantic_extra__` was incorrectly defined, causing schema generation errors
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #8752
Fix PR: https://github.com/pydantic/pydantic/pull/8659
First fixed release: 2.6.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.37

Discussion

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

Jump to Sources Open on GitHub

“@KasperZutterman, This should be fixed on main, thanks to @alexmojaki's work in https://github.com/pydantic/pydantic/pull/8659.”

@sydney-runkle · 2024-02-07 · confirmation · source

Failure Signature (Search String)

class Test(BaseModel):

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/Users/kasperzutterman/repositories/otainsight/transformations/modules/integrations/transformations/pms/tests/hotelkey/test3.py", line 6, in <module>
    class Test(BaseModel):
  File "/Users/kasperzutterman/.pyenv/versions/3.10.12/envs/pydantic/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 183, in __new__
    complete_model_class(
  File "/Users/kasperzutterman/.pyenv/versions/3.10.12/envs/pydantic/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 517, in complete_model_class
    schema = cls.__get_pydantic_core_schema__(cls, handler)
  File "/Users/kasperzutterman/.pyenv/versions/3.10.12/envs/pydantic/lib/python3.10/site-packages/pydantic/main.py", line 584, in __get_pydantic_core_schema__
    return __handler(__source)
  File "/Users/kasperzutterman/.pyenv/versions/3.10.12/envs/pydantic/lib/python3.10/site-packages/pydantic/_internal/_schema_generation_shared.py", line 82, in __call__
    schema = self._handler(__source_type)
  File "/Users/kasperzutterman/.pyenv/versions/3.10.12/envs/pydantic/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 499, in generate_schema
    schema = self._generate_schema(obj)
  File "/Users/kasperzutterman/.pyenv/versions/3.10.12/envs/pydantic/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 73
... (truncated) ...

Minimal Reproduction

repro.py

from __future__ import annotations  # <- removing this line solves the problem

from pydantic import BaseModel, ConfigDict


class Test(BaseModel):
    model_config = ConfigDict(extra='allow')
    __pydantic_extra__: dict[str, str]

Environment

Python: 3.10
Pydantic: 2

What Broke

Models with `__pydantic_extra__` annotation fail to generate schemas, leading to runtime errors.

Why It Broke

The type annotation for `__pydantic_extra__` was incorrectly defined, causing schema generation errors

Fix Options (Details)

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

pip install pydantic==2.6.0

When NOT to use: Do not use this fix if your model does not include `__pydantic_extra__`.

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/8659

First fixed release: 2.6.0

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

When NOT to Use This Fix

Do not use this fix if your model does not include `__pydantic_extra__`.

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
2.6.0	Fixed

Related Issues

No related fixes found.

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Related clusters: Data consistency OpenAPI schema Serialization

Sources

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

Pydantic `from __future__ import annotations` causes `__pydantic_extra__` type annotation error. (Fix)