Pydantic Recent `typing_extensions.TypeAliasType` backport

The Fix

pip install pydantic==1.10.19

Based on closed pydantic/pydantic issue #10711 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -12,10 +12,10 @@
 from pydantic_core import CoreSchema, core_schema
 from pydantic_core import validate_core_schema as _validate_core_schema
-from typing_extensions import TypeAliasType, TypeGuard, get_args, get_origin
+from typing_extensions import TypeGuard, get_args, get_origin

repro.py

# Cause
from typing_extensions import TypeAliasType
type Int = int  # creates typing.TypeAliasType
assert isinstance(Int, TypeAliasType) # fails

# Failing tests:

#  tests/test_forward_ref.py:1261 test_class_locals_are_kept_during_schema_generation
from pydantic import BaseModel
class Model(BaseModel):
        type Test = int
        a: 'Test | Forward'

# tests/test_edge_cases.py:2875 test_nested_type_statement
from pydantic import BaseModel
class A(BaseModel):
        type Int = int
        a: 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==1.10.19\nWhen NOT to use: Do not apply this fix if using versions of typing_extensions prior to the backport.\n\n

Why This Fix Works in Production

Trigger: Recent `typing_extensions.TypeAliasType` backport causing tests to fail.
Mechanism: Recent changes in typing_extensions introduced TypeAliasType, causing compatibility issues with Pydantic
Why the fix works: Adds support for the recent `typing_extensions.TypeAliasType` that was causing tests to fail. (first fixed release: 1.10.19).

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 3.12 in real deployments (not just unit tests).
Recent changes in typing_extensions introduced TypeAliasType, causing compatibility issues with Pydantic
Production symptom (often without a traceback): Recent `typing_extensions.TypeAliasType` backport causing tests to fail.

Proof / Evidence

GitHub issue: #10711
Fix PR: https://github.com/pydantic/pydantic/pull/10713
First fixed release: 1.10.19
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.56

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 See the related issue https://github.com/python/typing_extensions/issues/493#issuecomment-2437746930 and PR https://github.com/python/typing_extensions/pull/477 w”

Issue thread · issue description · source

Failure Signature (Search String)

Recent `typing_extensions.TypeAliasType` backport causing tests to fail.
assert isinstance(Int, TypeAliasType) # fails

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Recent `typing_extensions.TypeAliasType` backport causing tests to fail.
assert isinstance(Int, TypeAliasType) # fails

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Recent `typing_extensions.TypeAliasType` backport causing tests to fail.
assert isinstance(Int, TypeAliasType) # fails

Minimal Reproduction

repro.py

# Cause
from typing_extensions import TypeAliasType
type Int = int  # creates typing.TypeAliasType
assert isinstance(Int, TypeAliasType) # fails

# Failing tests:

#  tests/test_forward_ref.py:1261 test_class_locals_are_kept_during_schema_generation
from pydantic import BaseModel
class Model(BaseModel):
        type Test = int
        a: 'Test | Forward'

# tests/test_edge_cases.py:2875 test_nested_type_statement
from pydantic import BaseModel
class A(BaseModel):
        type Int = int
        a: Int

Environment

Python: 3.12
Pydantic: 2

What Broke

Tests fail for Pydantic models using TypeAliasType, impacting CI/CD pipelines.

Why It Broke

Recent changes in typing_extensions introduced TypeAliasType, causing compatibility issues with Pydantic

Fix Options (Details)

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

pip install pydantic==1.10.19

When NOT to use: Do not apply this fix if using versions of typing_extensions prior to the backport.

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/10713

First fixed release: 1.10.19

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

When NOT to Use This Fix

Do not apply this fix if using versions of typing_extensions prior to the backport.

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
1.10.19	Fixed

Related Issues

No related fixes found.

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Related clusters: Configuration error OpenAPI schema Serialization

Sources

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

Pydantic Recent `typing_extensions.TypeAliasType` backport causing tests to fail. (Fix)