Pydantic TypeError: ForwardRef._evaluate() missing 1

The Fix

pip install pydantic==1.10.16

Based on closed pydantic/pydantic issue #10747 · 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

@@ -63,7 +63,9 @@ def evaluate_forwardref(type_: ForwardRef, globalns: Any, localns: Any) -> Any:
         # Even though it is the right signature for python 3.9, mypy complains with
         # `error: Too many arguments for "_evaluate" of "ForwardRef"` hence the cast...
-        return cast(Any, type_)._evaluate(globalns, localns, set())
+        # Python 3.13/3.12.4+ made `recursive_guard` a kwarg, so name it explicitly to avoid:
+        # TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: 'recursive_guard'

repro.py

pydantic version: 2.9.2
    pydantic-core version: 2.23.4
      pydantic-core build: profile=release pgo=false
             install path: C:\work\ASI-DRI-Copilot\.venv\Lib\site-packages\pydantic
           python version: 3.12.7 (tags/v3.12.7:0b05ead, Oct  1 2024, 03:06:41) [MSC v.1941 64 bit (AMD64)]
                 platform: Windows-11-10.0.26100-SP0
         related packages: fastapi-0.115.4 mypy-1.13.0 pydantic-settings-2.6.0 typing_extensions-4.12.2
                   commit: unknown

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==1.10.16\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\n

Why This Fix Works in Production

Trigger: TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: 'recursive_guard' still occurs with v2.9.2 on Python 3.12.7
Mechanism: Specifies 'recursive_guard' as a keyword argument in the 'ForwardRef._evaluate' method to resolve a TypeError that occurs in Python 3.12.4 and later.
Why the fix works: Specifies 'recursive_guard' as a keyword argument in the 'ForwardRef._evaluate' method to resolve a TypeError that occurs in Python 3.12.4 and later. (first fixed release: 1.10.16).

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 3.12.7 in real deployments (not just unit tests).
Surfaces as: TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: 'recursive_guard' still occurs with v2.9.2 on Python 3.12.7

Proof / Evidence

GitHub issue: #10747
Fix PR: https://github.com/pydantic/pydantic/pull/9612
First fixed release: 1.10.16
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.46

Discussion

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

Jump to Sources Open on GitHub

“Seems like an env issue on your end. Here's the source code on 2.9.2: https://github.com/pydantic/pydantic/blob/7cedbfb03df82ac55c844c97e6f975359cb51bb9/pydantic/v1/typing.py#L63-L68”

@Viicos · 2024-10-31 · source

“Thank you for responding. However, it's not clear to me (sorry, Python n00b) and there's no suitable guidance documented elsewhere, on how to resolve this...…”

@johnazariah · 2024-10-31 · source

“The best way for you would be to recreate your venv, I can't provide more help here.”

@Viicos · 2024-10-31 · source

“Thank you! Recreating the venv didn't work, but I did a clean reinstall and the problem went away”

@johnazariah · 2024-10-31 · source

Failure Signature (Search String)

TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: 'recursive_guard' still occurs with v2.9.2 on Python 3.12.7

Error Message

Stack trace

error.txt

Error Message
-------------
TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: 'recursive_guard' still occurs with v2.9.2 on Python 3.12.7

Minimal Reproduction

repro.py

pydantic version: 2.9.2
    pydantic-core version: 2.23.4
      pydantic-core build: profile=release pgo=false
             install path: C:\work\ASI-DRI-Copilot\.venv\Lib\site-packages\pydantic
           python version: 3.12.7 (tags/v3.12.7:0b05ead, Oct  1 2024, 03:06:41) [MSC v.1941 64 bit (AMD64)]
                 platform: Windows-11-10.0.26100-SP0
         related packages: fastapi-0.115.4 mypy-1.13.0 pydantic-settings-2.6.0 typing_extensions-4.12.2
                   commit: unknown

Environment

Python: 3.12.7
Pydantic: 2

Fix Options (Details)

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

pip install pydantic==1.10.16

When NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.

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/9612

First fixed release: 1.10.16

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

When NOT to Use This Fix

Do not use if it changes public behavior or if the failure cannot be reproduced.

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
1.10.16	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 TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: (Fix)