Pydantic Private model attributes handled incorrectly by

The Fix

pip install pydantic==2.7.2

Based on closed pydantic/pydantic issue #9048 · 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

@@ -33,12 +33,14 @@
     from ..fields import Field as PydanticModelField
     from ..fields import FieldInfo, ModelPrivateAttr
+    from ..fields import PrivateAttr as PydanticModelPrivateAttr
     from ..main import BaseModel
 else:

repro.py

from pydantic import BaseModel


class MyModel(BaseModel):
    _private_attr: str


thing = MyModel()
print(thing.model_dump())

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==2.7.2\nWhen NOT to use: This fix should not be applied if the model relies on private attributes being exposed in the constructor.\n\n

Why This Fix Works in Production

Trigger: KeyError: '_private_attr'
Mechanism: Private model attributes were incorrectly included in the __init__ function signature, causing type checker errors
Why the fix works: Addresses the issue of private model attributes being incorrectly handled by type checkers by adding `PrivateAttr` to the list of field specifiers in Pydantic. (first fixed release: 2.7.2).

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

Shows up under Python 3.9 in real deployments (not just unit tests).
Private model attributes were incorrectly included in the __init__ function signature, causing type checker errors
Surfaces as: KeyError: '_private_attr'

Proof / Evidence

GitHub issue: #9048
Fix PR: https://github.com/pydantic/pydantic/pull/9293
First fixed release: 2.7.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.77

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: 2.7.2
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

“@TeeSeal I ran into the same issue. Since https://github.com/pydantic/pydantic/pull/9293 was merged, I was now able to solve the pyright issue by marking the attribute as…”

@mvernacc · 2024-08-16 · confirmation · source

“Closing as per https://github.com/pydantic/pydantic/issues/9048#issuecomment-2294362155.”

@Viicos · 2025-01-06 · confirmation · source

“@mvernacc > I ran into the same issue”

@TeeSeal · 2024-08-19 · confirmation · source

“@quentin-ag static type checkers _do not_ understand annotated metadata. Read more here.”

@Viicos · 2025-09-13 · source

Failure Signature (Search String)

KeyError: '_private_attr'

Error Message

Stack trace

error.txt

Error Message
-------------
KeyError: '_private_attr'

Minimal Reproduction

repro.py

from pydantic import BaseModel


class MyModel(BaseModel):
    _private_attr: str


thing = MyModel()
print(thing.model_dump())

Environment

Python: 3.9
Pydantic: 2

What Broke

Type checkers report errors when instantiating models with private attributes, leading to confusion for developers.

Why It Broke

Private model attributes were incorrectly included in the __init__ function signature, causing type checker errors

Fix Options (Details)

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

pip install pydantic==2.7.2

When NOT to use: This fix should not be applied if the model relies on private attributes being exposed in the constructor.

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/9293

First fixed release: 2.7.2

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

When NOT to Use This Fix

This fix should not be applied if the model relies on private attributes being exposed in the constructor.

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
2.7.2	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 Private model attributes handled incorrectly by type checkers (Fix)