Pydantic Unable to subclass model with

The Fix

pip install pydantic==2.9.2

Based on closed pydantic/pydantic issue #10384 · 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

@@ -690,7 +690,7 @@ def set_deprecated_descriptors(cls: type[BaseModel]) -> None:
 
 class _DeprecatedFieldDescriptor:
-    """Data descriptor used to emit a runtime deprecation warning before accessing a deprecated field.
+    """Read-only data descriptor used to emit a runtime deprecation warning before accessing a deprecated field.

repro.py

from pydantic import BaseModel, computed_field


class A(BaseModel):
    name: str

    @computed_field(deprecated=True)
    def resolved_name(self) -> str:
        return self.name.upper()


class B(A): ...

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==2.9.2\nWhen NOT to use: This fix should not be applied if the model does not contain deprecated computed fields.\n\n

Why This Fix Works in Production

Trigger: return getattr(tp, name)
Mechanism: Subclassing models with deprecated computed fields caused an AttributeError during model construction
Why the fix works: Fix class access of deprecated computed fields to allow subclassing models with deprecated computed fields. (first fixed release: 2.9.2).

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).
Subclassing models with deprecated computed fields caused an AttributeError during model construction
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #10384
Fix PR: https://github.com/pydantic/pydantic/pull/10391
First fixed release: 2.9.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.37

Discussion

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

Jump to Sources Open on GitHub

“Thanks for the bug report, I'll work on fix.”

@Viicos · 2024-09-11 · source

Failure Signature (Search String)

return getattr(tp, name)

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "~/.pyenv/versions/bikeshed/lib/python3.11/site-packages/pydantic/_internal/_decorators.py", line 382, in get_attribute_from_bases
    return getattr(tp, name)
           ^^^^^^^^^^^^^^^^^
  File "~/.pyenv/versions/bikeshed/lib/python3.11/site-packages/pydantic/_internal/_model_construction.py", line 262, in __getattr__
    raise AttributeError(item)
AttributeError: resolved_name

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "~/example.py", line 12, in <module>
    class B(A): ...
  File "~/.pyenv/versions/bikeshed/lib/python3.11/site-packages/pydantic/_internal/_model_construction.py", line 154, in __new__
    cls.__pydantic_decorators__ = DecoratorInfos.build(cls)
                                  ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.pyenv/versions/bikeshed/lib/python3.11/site-packages/pydantic/_internal/_decorators.py", line 450, in build
    res.computed_fields.update({k: v.bind_to_cls(model_dc) for k, v in existing.computed_fields.items()})
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/.pyenv/versions/bikeshed/lib/python3.11/site-packages/pydantic/_internal/_decorators.py", line 450, in <dictcomp>
    res.computed_fields.update({k: v.bind_to_cls(model_dc) for k, v in existing.computed_fields.items()
... (truncated) ...

Minimal Reproduction

repro.py

from pydantic import BaseModel, computed_field


class A(BaseModel):
    name: str

    @computed_field(deprecated=True)
    def resolved_name(self) -> str:
        return self.name.upper()


class B(A): ...

Environment

Python: 3.11
Pydantic: 2

What Broke

Attempting to subclass a model resulted in runtime errors, preventing proper model usage.

Why It Broke

Subclassing models with deprecated computed fields caused an AttributeError during model construction

Fix Options (Details)

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

pip install pydantic==2.9.2

When NOT to use: This fix should not be applied if the model does not contain deprecated computed fields.

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/10391

First fixed release: 2.9.2

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 contain deprecated computed fields.

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
2.9.2	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 Unable to subclass model with @computed_field(deprecated=True) (Fix)