Pydantic `FieldInfo.__repr_args__` ignoring field's default

The Fix

pip install pydantic==2.6.2

Based on closed pydantic/pydantic issue #8629 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -574,7 +574,9 @@ def __repr_args__(self) -> ReprArgs:
             if s == 'serialization_alias' and self.serialization_alias == self.alias:
                 continue
-            if s == 'default_factory' and self.default_factory is not None:
+            if s == 'default' and self.default is not PydanticUndefined:
+                yield 'default', self.default

repro.py

from pprint import pprint

import pydantic


class Foo(pydantic.BaseModel):
    a: str = pydantic.Field("ADEF", alias="A")
    b: int = pydantic.Field(..., alias="B")
    c: str | None = pydantic.Field(None, alias="C")


pprint(Foo.model_fields)

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==2.6.2\nWhen NOT to use: This fix should not be used if the default value behavior is critical for existing model definitions.\n\n

Why This Fix Works in Production

Trigger: This is more a quality of live improvement than anything else. With the proposed change, it's easier to inspect model definitions at a glance (and it's also…
Mechanism: The __repr_args__ method in FieldInfo does not include the default value when explicitly set to None
Why the fix works: Fixes the issue where FieldInfo.__repr_args__ does not include the default value when it is explicitly set to None. (first fixed release: 2.6.2).

Why This Breaks in Prod

Shows up under Python 3.11 in real deployments (not just unit tests).
The __repr_args__ method in FieldInfo does not include the default value when explicitly set to None
Production symptom (often without a traceback): This is more a quality of live improvement than anything else. With the proposed change, it's easier to inspect model definitions at a glance (and it's also less confusing)

Proof / Evidence

GitHub issue: #8629
Fix PR: https://github.com/pydantic/pydantic/pull/8801
First fixed release: 2.6.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.61

Discussion

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

Jump to Sources Open on GitHub

“@Evenfire, Thanks for pointing this out! I agree with your suggested change. Please open a PR, and I'd be happy to review :).”

@sydney-runkle · 2024-01-25 · source

“@Evenfire, This issue is quite related - https://github.com/pydantic/pydantic/issues/8634. Would you be interested in taking a stab at a fix for that one as well? Thanks…”

@sydney-runkle · 2024-01-25 · source

“@sydney-runkle I'll open a PR for this issue as soon as I have few minutes.”

@Evenfire · 2024-01-26 · source

Failure Signature (Search String)

This is more a quality of live improvement than anything else. With the proposed change, it's easier to inspect model definitions at a glance (and it's also less confusing)

Copy-friendly signature

signature.txt

Failure Signature
-----------------
This is more a quality of live improvement than anything else. With the proposed change, it's easier to inspect model definitions at a glance (and it's also less confusing)
python version: 3.11.7 (main, Jan  7 2024, 10:09:49) [Clang 15.0.0 (clang-1500.1.0.2.5)]

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
This is more a quality of live improvement than anything else. With the proposed change, it's easier to inspect model definitions at a glance (and it's also less confusing)
python version: 3.11.7 (main, Jan  7 2024, 10:09:49) [Clang 15.0.0 (clang-1500.1.0.2.5)]

Minimal Reproduction

repro.py

from pprint import pprint

import pydantic


class Foo(pydantic.BaseModel):
    a: str = pydantic.Field("ADEF", alias="A")
    b: int = pydantic.Field(..., alias="B")
    c: str | None = pydantic.Field(None, alias="C")


pprint(Foo.model_fields)

Environment

Python: 3.11
Pydantic: 2

What Broke

FieldInfo representation does not show default values, causing confusion during model inspection.

Why It Broke

The __repr_args__ method in FieldInfo does not include the default value when explicitly set to None

Fix Options (Details)

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

pip install pydantic==2.6.2

When NOT to use: This fix should not be used if the default value behavior is critical for existing model definitions.

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/8801

First fixed release: 2.6.2

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

When NOT to Use This Fix

This fix should not be used if the default value behavior is critical for existing model definitions.

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
2.6.2	Fixed

Related Issues

No related fixes found.

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Related clusters: Configuration error Data consistency OpenAPI schema

Sources

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

Pydantic `FieldInfo.__repr_args__` ignoring field's default value when set to `None` explicitly (Fix)