Pydantic () `Field` info specified through pep 695 type

The Fix

pip install pydantic==2.11.0

Based on closed pydantic/pydantic issue #11552 · 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

@@ -322,6 +322,9 @@ By leveraging the new [`type` statement](https://typing.readthedocs.io/en/latest
     Only metadata that can be applied to the annotated type itself is allowed
     (e.g. [validation constraints](./fields.md#field-constraints) and JSON metadata).
+    Trying to support field-specific metadata would require eagerly inspecting the
+    type alias's [`__value__`][typing.TypeAliasType.__value__], and as such Pydantic
+    wouldn't be able to have the alias stored as a JSON Schema definition.

repro.py

from typing import Annotated

from pydantic import BaseModel, Field

A = Annotated[int, Field(alias="aa")]
type B = Annotated[int, Field(alias="bb")]


class M(BaseModel):
    a: A
    b: B


M.model_validate({"aa": 1, "bb": 2})

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==2.11.0\nWhen NOT to use: This fix should not be used if backward compatibility with older Pydantic versions is required.\n\n

Why This Fix Works in Production

Trigger: pydantic_core._pydantic_core.ValidationError: 1 validation error for M
Mechanism: Field-specific metadata in PEP 695 type aliases is not handled correctly by Pydantic
Why the fix works: Fixes the handling of field-specific metadata in PEP 695 type aliases, ensuring proper JSON Schema generation. (first fixed release: 2.11.0).

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

Field-specific metadata in PEP 695 type aliases is not handled correctly by Pydantic
Surfaces as: pydantic_core._pydantic_core.ValidationError: 1 validation error for M

Proof / Evidence

GitHub issue: #11552
Fix PR: https://github.com/pydantic/pydantic/pull/11570
First fixed release: 2.11.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.55

Discussion

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

Jump to Sources Open on GitHub

“This is expected, see https://github.com/pydantic/pydantic/pull/11475 and the documentation that will be published in 2.11.”

@Viicos · 2025-03-14 · source

“oh, that's disappointing”

@KotlinIsland · 2025-03-14 · source

“See https://github.com/pydantic/pydantic/issues/11467 for more context as well”

@Viicos · 2025-03-14 · source

“I opened https://github.com/pydantic/pydantic/pull/11570.”

@Viicos · 2025-03-17 · source

Failure Signature (Search String)

pydantic_core._pydantic_core.ValidationError: 1 validation error for M

Error Message

Stack trace

error.txt

Error Message
-------------
pydantic_core._pydantic_core.ValidationError: 1 validation error for M
b
  Field required [type=missing, input_value={'aa': 1, 'bb': 2}, input_type=dict]

Minimal Reproduction

repro.py

from typing import Annotated

from pydantic import BaseModel, Field

A = Annotated[int, Field(alias="aa")]
type B = Annotated[int, Field(alias="bb")]


class M(BaseModel):
    a: A
    b: B


M.model_validate({"aa": 1, "bb": 2})

Environment

Pydantic: 2

What Broke

Validation errors occur when using PEP 695 type aliases with field-specific metadata.

Why It Broke

Field-specific metadata in PEP 695 type aliases is not handled correctly by Pydantic

Fix Options (Details)

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

pip install pydantic==2.11.0

When NOT to use: This fix should not be used if backward compatibility with older Pydantic versions is required.

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/11570

First fixed release: 2.11.0

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

When NOT to Use This Fix

This fix should not be used if backward compatibility with older Pydantic versions is required.

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
2.11.0	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 () `Field` info specified through pep 695 type alias statement is not handled correctly (Fix)