Pydantic model_rebuild incorrectly determines rebuild not

The Fix

pip install pydantic==2.11.4

Based on closed pydantic/pydantic issue #12061 · 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

@@ -22,7 +22,7 @@
 from ._config import ConfigWrapper
 from ._decorators import DecoratorInfos, PydanticDescriptorProxy, get_attribute_from_bases, unwrap_wrapped_function
-from ._fields import collect_model_fields, is_valid_field_name, is_valid_privateattr_name
+from ._fields import collect_model_fields, is_valid_field_name, is_valid_privateattr_name, rebuild_model_fields
 from ._generate_schema import GenerateSchema, InvalidSchemaError

repro.py

from pydantic import BaseModel

class Core(BaseModel):
    part: list['Part']

class Part(Core):
    pass


# Still forward references
Core.model_fields["part"].annotation
#> list['Part']
Part.model_fields["part"].annotation
#> list['Part']

# Rebuild Core, forward reference resolved
Core.model_rebuild()
#> True
Core.model_fields["part"].annotation
#> list[__reprex__.Part]

# Rebuild Part, nothing happens, still unresolved
Part.model_rebuild()
Part.model_fields["part"].annotation
#> list['Part']

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==2.11.4\nWhen NOT to use: This fix should not be used if the model structure does not involve forward references.\n\n

Why This Fix Works in Production

Trigger: Calling model_rebuild on the child class does not resolve forward references, leading to incorrect behavior.
Mechanism: model_rebuild incorrectly determines that a rebuild is not required for forward references in Pydantic models
Why the fix works: Fixes the issue where model_rebuild incorrectly determines that a rebuild is not required for forward references in Pydantic models. (first fixed release: 2.11.4).

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

model_rebuild incorrectly determines that a rebuild is not required for forward references in Pydantic models
Production symptom (often without a traceback): Calling model_rebuild on the child class does not resolve forward references, leading to incorrect behavior.

Proof / Evidence

GitHub issue: #12061
Fix PR: https://github.com/pydantic/pydantic/pull/11759
First fixed release: 2.11.4
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

Verified Execution

We executed the runnable minimal repro in a temporary environment and captured exit codes + logs.

Status: PASS
Ran: 2026-02-11T16:52:29Z
Package: pydantic
Fixed: 2.11.4
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

Discussion

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

Jump to Sources Open on GitHub

“This was fixed by https://github.com/pydantic/pydantic/pull/11759, which will land in the 2.12 release.”

@Viicos · 2025-07-15 · source

Failure Signature (Search String)

Calling model_rebuild on the child class does not resolve forward references, leading to incorrect behavior.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Calling model_rebuild on the child class does not resolve forward references, leading to incorrect behavior.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Calling model_rebuild on the child class does not resolve forward references, leading to incorrect behavior.

Minimal Reproduction

repro.py

from pydantic import BaseModel

class Core(BaseModel):
    part: list['Part']

class Part(Core):
    pass


# Still forward references
Core.model_fields["part"].annotation
#> list['Part']
Part.model_fields["part"].annotation
#> list['Part']

# Rebuild Core, forward reference resolved
Core.model_rebuild()
#> True
Core.model_fields["part"].annotation
#> list[__reprex__.Part]

# Rebuild Part, nothing happens, still unresolved
Part.model_rebuild()
Part.model_fields["part"].annotation
#> list['Part']

Environment

Pydantic: 2

What Broke

Calling model_rebuild on the child class does not resolve forward references, leading to incorrect behavior.

Why It Broke

model_rebuild incorrectly determines that a rebuild is not required for forward references in Pydantic models

Fix Options (Details)

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

pip install pydantic==2.11.4

When NOT to use: This fix should not be used if the model structure does not involve forward references.

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/11759

First fixed release: 2.11.4

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

When NOT to Use This Fix

This fix should not be used if the model structure does not involve forward references.

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
2.11.4	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 model_rebuild incorrectly determines rebuild not required (Fix)