Pydantic Signature of "__replace_

The Fix

pip install pydantic==2.10.2

Based on closed pydantic/pydantic issue #10970 · 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

@@ -871,10 +871,6 @@ def __deepcopy__(self, memo: dict[int, Any] | None = None) -> Self:
         return m
 
-    def __replace__(self, **changes: Any) -> Self:
-        """Creates a new instance of the model, replacing fields with values from changes. Relevant for v3.13+."""
-        return self.model_copy(update=changes)

repro.py

Signature of "__replace__" incompatible with supertype "BaseModel"
     Superclass:
         def __replace__(self, **changes: Any) -> Pets
     Subclass:
         def __replace__(*, root: list[str] = ...) -> Pets

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==2.10.2\nWhen NOT to use: Do not apply this fix if your project relies on the original `__replace__` behavior of `BaseModel`.\n\n

Why This Fix Works in Production

Trigger: Signature of "__replace__" incompatible - RootModel
Mechanism: The `__replace__` method in `RootModel` conflicts with the superclass `BaseModel` due to differing signatures
Why the fix works: Hides the `BaseModel.__replace__` definition from type checkers to resolve compatibility issues with mypy and the Pydantic plugin. (first fixed release: 2.10.2).

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 3.13 in real deployments (not just unit tests).
The `__replace__` method in `RootModel` conflicts with the superclass `BaseModel` due to differing signatures
Production symptom (often without a traceback): Signature of "__replace__" incompatible - RootModel

Proof / Evidence

GitHub issue: #10970
Fix PR: https://github.com/pydantic/pydantic/pull/10979
First fixed release: 2.10.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.67

Discussion

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

Jump to Sources Open on GitHub

“Closely related: https://github.com/pydantic/pydantic/issues/10699 I'm not able to repro this issue with https://docs.pydantic.dev/latest/concepts/models/#rootmodel-and-custom-root-types however. Do you have a MRE available?”

@Viicos · 2024-11-25 · repro detail · source

“Thanks for the clear repro steps. I'm now able to reproduce, and will investigate tomorrow.”

@Viicos · 2024-11-25 · repro detail · source

“EDIT: ~~I can try to create one, yes~~ I created a repo here https://github.com/jorgebodega/pydantic-10970, and tested it with a friend and also has the problem”

@jorgebodega · 2024-11-25 · source

“If the core issue is specific to RootModel, perhaps consider updating the title of the issue.”

@mpkocher · 2024-11-26 · source

Failure Signature (Search String)

Signature of "__replace__" incompatible - RootModel
It's raising an error like this:

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Signature of "__replace__" incompatible - RootModel
It's raising an error like this:

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Signature of "__replace__" incompatible - RootModel
It's raising an error like this:

Minimal Reproduction

repro.py

Signature of "__replace__" incompatible with supertype "BaseModel"
     Superclass:
         def __replace__(self, **changes: Any) -> Pets
     Subclass:
         def __replace__(*, root: list[str] = ...) -> Pets

Environment

Python: 3.13
Pydantic: 2

What Broke

Type checking fails with mypy, causing development delays and potential integration issues.

Why It Broke

The `__replace__` method in `RootModel` conflicts with the superclass `BaseModel` due to differing signatures

Fix Options (Details)

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

pip install pydantic==2.10.2

When NOT to use: Do not apply this fix if your project relies on the original `__replace__` behavior of `BaseModel`.

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/10979

First fixed release: 2.10.2

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

When NOT to Use This Fix

Do not apply this fix if your project relies on the original `__replace__` behavior of `BaseModel`.

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
2.10.2	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 Signature of "__replace__" incompatible - RootModel (Fix)