Pydantic Wrong parent namespace fetched when using an

The Fix

pip install pydantic==2.10.1

Based on closed pydantic/pydantic issue #10892 · 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

@@ -4,6 +4,7 @@
 import sys
 from dataclasses import is_dataclass
+from types import FrameType
 from typing import (
     Any,

repro.py

from pydantic import TypeAdapter

TAInt = TypeAdapter[int]
TAInt.__class__
#> typing._GenericAlias

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==2.10.1\nWhen NOT to use: This fix should not be used if the type adaptation relies on the behavior of `_GenericAlias`.\n\n

Why This Fix Works in Production

Trigger: assert TypeAdapter[int]('Text').core_schema == {'type': 'int'}
Mechanism: The wrong parent frame is fetched due to the proxy behavior of `_GenericAlias` in `TypeAdapter` instantiation
Why the fix works: Fixes the issue of wrong parent namespace being fetched when using an explicitly parametrized `TypeAdapter`. (first fixed release: 2.10.1).

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

The wrong parent frame is fetched due to the proxy behavior of `_GenericAlias` in `TypeAdapter` instantiation
Production symptom (often without a traceback): assert TypeAdapter[int]('Text').core_schema == {'type': 'int'}

Proof / Evidence

GitHub issue: #10892
Fix PR: https://github.com/pydantic/pydantic/pull/10893
First fixed release: 2.10.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.75

Discussion

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

Jump to Sources Open on GitHub

“This is a nice write up to clarify the core issue. When the parameterized type is inconsistent, is a runtime error raised? Or is this…”

@mpkocher · 2024-11-20 · source

“> When the parameterized type is inconsistent, is a runtime error raised? Or is this error mode on the static analysis tools side of the…”

@Viicos · 2024-11-21 · source

Failure Signature (Search String)

assert TypeAdapter[int]('Text').core_schema == {'type': 'int'}
When the parameterized type is inconsistent, is a runtime error raised? Or is this error mode on the static analysis tools side of the fence?

Copy-friendly signature

signature.txt

Failure Signature
-----------------
assert TypeAdapter[int]('Text').core_schema == {'type': 'int'}
When the parameterized type is inconsistent, is a runtime error raised? Or is this error mode on the static analysis tools side of the fence?

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
assert TypeAdapter[int]('Text').core_schema == {'type': 'int'}
When the parameterized type is inconsistent, is a runtime error raised? Or is this error mode on the static analysis tools side of the fence?

Minimal Reproduction

repro.py

from pydantic import TypeAdapter

TAInt = TypeAdapter[int]
TAInt.__class__
#> typing._GenericAlias

Environment

Pydantic: 2

What Broke

Incorrect type validation occurs, leading to assertion errors in type adaptation.

Why It Broke

The wrong parent frame is fetched due to the proxy behavior of `_GenericAlias` in `TypeAdapter` instantiation

Fix Options (Details)

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

pip install pydantic==2.10.1

When NOT to use: This fix should not be used if the type adaptation relies on the behavior of `_GenericAlias`.

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/10893

First fixed release: 2.10.1

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

When NOT to Use This Fix

This fix should not be used if the type adaptation relies on the behavior of `_GenericAlias`.

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
2.10.1	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 Wrong parent namespace fetched when using an explicitly parametrized `TypeAdapter` (Fix)