Pydantic __pydantic_complete__ is not updated when

The Fix

pip install pydantic==2.9.0

Based on closed pydantic/pydantic issue #10284 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -191,6 +191,7 @@ def validated_setattr(instance: Any, field: str, value: str, /) -> None:
         cls.__setattr__ = validated_setattr.__get__(None, cls)  # type: ignore
 
+    cls.__pydantic_complete__ = True
     return True

repro.py

from pydantic.dataclasses import dataclass, rebuild_dataclass

@dataclass
class Point:
    x: float
    y: float
    color: 'Color'

print(Point.__pydantic_complete__)  # False: Color is not known yet

print(rebuild_dataclass(Point, raise_errors=False))  # False: the dataclass can't be rebuilt

# Now, we define color
@dataclass
class Color:
    name: str

print(rebuild_dataclass(Point))  # True: the dataclass has been rebuilt!

print(Point(x=12, y=-2, color={"name": "red"}))  # Check that the dataclass works correctly

# This should be True now that the dataclass has been rebuilt
# However, it is still False
print(Point.__pydantic_complete__)

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==2.9.0\nWhen NOT to use: This fix should not be applied if the behavior of `__pydantic_complete__` is intentionally designed to remain unchanged.\n\n

Why This Fix Works in Production

Trigger: print(rebuild_dataclass(Point, raise_errors=False)) # False: the dataclass can't be rebuilt
Mechanism: The `__pydantic_complete__` field is not updated after calling `rebuild_dataclass`
Why the fix works: Ensure `__pydantic_complete__` is set when rebuilding dataclasses. (first fixed release: 2.9.0).

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 3.10 in real deployments (not just unit tests).
The `__pydantic_complete__` field is not updated after calling `rebuild_dataclass`
Production symptom (often without a traceback): print(rebuild_dataclass(Point, raise_errors=False)) # False: the dataclass can't be rebuilt

Proof / Evidence

GitHub issue: #10284
Fix PR: https://github.com/pydantic/pydantic/pull/10291
First fixed release: 2.9.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
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: 2.9.0
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

False
False
True
Point(x=12.0, y=-2.0, color=Color(name='red'))
True

Discussion

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

Jump to Sources Open on GitHub

“Thanks for the bug report, pushing a fix.”

@Viicos · 2024-09-03 · source

Failure Signature (Search String)

print(rebuild_dataclass(Point, raise_errors=False)) # False: the dataclass can't be rebuilt

Copy-friendly signature

signature.txt

Failure Signature
-----------------
print(rebuild_dataclass(Point, raise_errors=False))  # False: the dataclass can't be rebuilt

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
print(rebuild_dataclass(Point, raise_errors=False))  # False: the dataclass can't be rebuilt

Minimal Reproduction

repro.py

from pydantic.dataclasses import dataclass, rebuild_dataclass

@dataclass
class Point:
    x: float
    y: float
    color: 'Color'

print(Point.__pydantic_complete__)  # False: Color is not known yet

print(rebuild_dataclass(Point, raise_errors=False))  # False: the dataclass can't be rebuilt

# Now, we define color
@dataclass
class Color:
    name: str

print(rebuild_dataclass(Point))  # True: the dataclass has been rebuilt!

print(Point(x=12, y=-2, color={"name": "red"}))  # Check that the dataclass works correctly

# This should be True now that the dataclass has been rebuilt
# However, it is still False
print(Point.__pydantic_complete__)

Environment

Python: 3.10
Pydantic: 2

What Broke

Repeated calls to `rebuild_dataclass` unnecessarily rebuild the dataclass, impacting performance.

Why It Broke

The `__pydantic_complete__` field is not updated after calling `rebuild_dataclass`

Fix Options (Details)

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

pip install pydantic==2.9.0

When NOT to use: This fix should not be applied if the behavior of `__pydantic_complete__` is intentionally designed to remain unchanged.

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/10291

First fixed release: 2.9.0

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

When NOT to Use This Fix

This fix should not be applied if the behavior of `__pydantic_complete__` is intentionally designed to remain unchanged.

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
2.9.0	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:data-consistency Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Configuration error OpenAPI schema Serialization

Sources

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

Pydantic __pydantic_complete__ is not updated when rebuilding dataclass (Fix)