Pydantic use_enum_values=True has no effect if another

The Fix

pip install pydantic==2.6.4

Based on closed pydantic/pydantic issue #8858 · 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

@@ -81,8 +81,6 @@ def get_json_schema(_, handler: GetJsonSchemaHandler) -> JsonSchemaValue:
         return core_schema.is_instance_schema(enum_type, metadata={'pydantic_js_functions': [get_json_schema]})
 
-    use_enum_values = config.get('use_enum_values', False)
-
     if len(cases) == 1:

repro.py

from pydantic import BaseModel, __version__ as pydantic_version
from enum import Enum


class MyEnum(str, Enum):
    A = 'a'


class MyModel(BaseModel, use_enum_values=True):
    my_enum: MyEnum


class OtherModel(BaseModel):
    also_my_enum: MyEnum


class Model(BaseModel):
    my_model: MyModel
    other_model: OtherModel


data = {'my_model': {'my_enum': 'a'}, 'other_model': {'also_my_enum': 'a'}}
print(f'{pydantic_version=}')
# pydantic_version='2.6.1'
print(Model.parse_obj(data))
# my_model=MyModel(my_enum=<MyEnum.A: 'a'>) other_model=OtherModel(also_my_enum=<MyEnum.A: '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==2.6.4\nWhen NOT to use: Do not apply this fix if all models using the enum should maintain their original behavior.\n\n

Why This Fix Works in Production

Trigger: If two separate models with different `use_enum_values` settings both have fields with the same enum, pydantic v2 doesn't use that enum's values in either…
Mechanism: The use_enum_values setting was not respected when multiple models used the same enum with different settings
Why the fix works: Fixes a regression where the use_enum_values setting in Pydantic v2 was not respected when multiple models used the same enum with different settings. (first fixed release: 2.6.4).

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

The use_enum_values setting was not respected when multiple models used the same enum with different settings
Production symptom (often without a traceback): If two separate models with different `use_enum_values` settings both have fields with the same enum, pydantic v2 doesn't use that enum's values in either model.

Proof / Evidence

GitHub issue: #8858
Fix PR: https://github.com/pydantic/pydantic/pull/8920
First fixed release: 2.6.4
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: 2.6.4
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

pydantic_version='2.6.4'
my_model=MyModel(my_enum=<MyEnum.A: 'a'>) other_model=OtherModel(also_my_enum=<MyEnum.A: 'a'>)

Discussion

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

Jump to Sources Open on GitHub

“@sydney-runkle I can try and look into this if it's still available 😄”

@NeevCohen · 2024-02-24 · source

“Ah, @dmontagu came up with a fix: https://github.com/pydantic/pydantic/pull/8920”

@sydney-runkle · 2024-02-29 · source

“@vaultah, Yep, looks like a bug. Thanks for reporting the regression. You're welcome to submit a PR with a fix, if you'd like. I'll add…”

@sydney-runkle · 2024-02-20 · source

“@sydney-runkle Awesome! Let me know if there's anything I can do to help out”

@NeevCohen · 2024-02-29 · source

Failure Signature (Search String)

If two separate models with different `use_enum_values` settings both have fields with the same enum, pydantic v2 doesn't use that enum's values in either model.
This is a regression from pydantic v1.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
If two separate models with different `use_enum_values` settings both have fields with the same enum, pydantic v2 doesn't use that enum's values in either model.
This is a regression from pydantic v1.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
If two separate models with different `use_enum_values` settings both have fields with the same enum, pydantic v2 doesn't use that enum's values in either model.
This is a regression from pydantic v1.

Minimal Reproduction

repro.py

from pydantic import BaseModel, __version__ as pydantic_version
from enum import Enum


class MyEnum(str, Enum):
    A = 'a'


class MyModel(BaseModel, use_enum_values=True):
    my_enum: MyEnum


class OtherModel(BaseModel):
    also_my_enum: MyEnum


class Model(BaseModel):
    my_model: MyModel
    other_model: OtherModel


data = {'my_model': {'my_enum': 'a'}, 'other_model': {'also_my_enum': 'a'}}
print(f'{pydantic_version=}')
# pydantic_version='2.6.1'
print(Model.parse_obj(data))
# my_model=MyModel(my_enum=<MyEnum.A: 'a'>) other_model=OtherModel(also_my_enum=<MyEnum.A: 'a'>)

Environment

Pydantic: 2

What Broke

Models failed to parse enum values correctly, leading to unexpected types in the output.

Why It Broke

The use_enum_values setting was not respected when multiple models used the same enum with different settings

Fix Options (Details)

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

pip install pydantic==2.6.4

When NOT to use: Do not apply this fix if all models using the enum should maintain their original behavior.

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/8920

First fixed release: 2.6.4

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

When NOT to Use This Fix

Do not apply this fix if all models using the enum should maintain their original behavior.

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
2.6.4	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 use_enum_values=True has no effect if another model with the same enum has (Fix)