Pydantic `__pydantic_extra__` type hint incompatible with

The Fix

pip install pydantic==2.6.0

Based on closed pydantic/pydantic issue #8647 · 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

Traceback (most recent call last):
  File "/tmp/pydantic/noworky.py", line 6, in <module>
    class Foo(BaseModel, extra="allow"):
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 182, in __new__
    complete_model_class(
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 491, in complete_model_class
    schema = cls.__get_pydantic_core_schema__(cls, handler)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/main.py", line 578, in __get_pydantic_core_schema__
    return __handler(__source)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_schema_generation_shared.py", line 82, in __call__
    schema = self._handler(__source_type)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 468, in generate_schema
    schema = self._generate_schema(obj)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 700, in _generate_schema
    schema = self._post_process_generated_schema(self._generate_schema_inner(obj))
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 722, in _generate_schema_inner
    return self._model_schema(obj)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 512, in _model_schema
    raise PydanticSchemaGenerationError(
pydantic.errors.PydanticSchemaGenerationError: The type annotation for `__pydantic_extra__` must be `Dict[str, ...]`

For further information visit https://errors.pydantic.dev/2.5/u/schema-for-unknown-type

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: This fix should not be used if the type hint is intentionally set to a non-dict type.\n\n

Why This Fix Works in Production

Trigger: class Foo(BaseModel, extra="allow"):
Mechanism: The type annotation for `__pydantic_extra__` is incorrectly treated as a string when using future annotations
Why the fix works: Handles the `__pydantic_extra__` annotation being a string or inherited, fixing the schema generation error when using future 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__` is incorrectly treated as a string when using future annotations
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #8647
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: 0.27

Discussion

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

Jump to Sources Open on GitHub

“@alexmojaki, Could you please take a look at this issue when you have a chance? Thanks!”

@sydney-runkle · 2024-01-28 · source

Failure Signature (Search String)

class Foo(BaseModel, extra="allow"):

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/tmp/pydantic/noworky.py", line 6, in <module>
    class Foo(BaseModel, extra="allow"):
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 182, in __new__
    complete_model_class(
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 491, in complete_model_class
    schema = cls.__get_pydantic_core_schema__(cls, handler)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/main.py", line 578, in __get_pydantic_core_schema__
    return __handler(__source)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_schema_generation_shared.py", line 82, in __call__
    schema = self._handler(__source_type)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 468, in generate_schema
    schema = self._generate_schema(obj)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 700, in _generate_schema
    schema = self._post_process_generated_schema(self._generate_schema_inner(obj))
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 722, in _generate_schema_inner
    return self._model_schema(obj)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_i
... (truncated) ...

Minimal Reproduction

repro.py

Traceback (most recent call last):
  File "/tmp/pydantic/noworky.py", line 6, in <module>
    class Foo(BaseModel, extra="allow"):
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 182, in __new__
    complete_model_class(
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 491, in complete_model_class
    schema = cls.__get_pydantic_core_schema__(cls, handler)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/main.py", line 578, in __get_pydantic_core_schema__
    return __handler(__source)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_schema_generation_shared.py", line 82, in __call__
    schema = self._handler(__source_type)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 468, in generate_schema
    schema = self._generate_schema(obj)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 700, in _generate_schema
    schema = self._post_process_generated_schema(self._generate_schema_inner(obj))
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 722, in _generate_schema_inner
    return self._model_schema(obj)
  File "/tmp/pydantic/venv/lib/python3.10/site-packages/pydantic/_internal/_generate_schema.py", line 512, in _model_schema
    raise PydanticSchemaGenerationError(
pydantic.errors.PydanticSchemaGenerationError: The type annotation for `__pydantic_extra__` must be `Dict[str, ...]`

For further information visit https://errors.pydantic.dev/2.5/u/schema-for-unknown-type

Environment

Python: 3.10
Pydantic: 2

What Broke

Users encounter schema generation errors when using `from __future__ import annotations`.

Why It Broke

The type annotation for `__pydantic_extra__` is incorrectly treated as a string when using future annotations

Fix Options (Details)

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

pip install pydantic==2.6.0

When NOT to use: This fix should not be used if the type hint is intentionally set to a non-dict type.

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

This fix should not be used if the type hint is intentionally set to a non-dict type.

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 `__pydantic_extra__` type hint incompatible with `from __future__ import annotations` (Fix)