Pydantic Circular ref error with `validate

The Fix

pip install pydantic==2.10.0

Based on closed pydantic/pydantic issue #10799 · 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

@@ -17,10 +17,12 @@
 from enum import Enum
 from fractions import Fraction
+from functools import partial
 from inspect import Parameter, _ParameterKind, signature
 from ipaddress import IPv4Address, IPv4Interface, IPv4Network, IPv6Address, IPv6Interface, IPv6Network

repro.py

pydantic version: 2.10.0b1
        pydantic-core version: 2.26.0
          pydantic-core build: profile=release pgo=false
                 install path: /Users/jpdephillips/.local/share/virtualenvs/iconic-DQE3a5P9/lib/python3.10/site-packages/pydantic
               python version: 3.10.0 (default, Mar  8 2024, 14:47:28) [Clang 14.0.0 (clang-1400.0.29.102)]
                     platform: macOS-14.1-x86_64-i386-64bit
             related packages: 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==2.10.0\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: ImportError: cannot import name 'VALIDATE_CALL_SUPPORTED_TYPES' from partially initialized module 'pydantic._internal._validate_call' (most likely due to a…
Mechanism: Circular import in the `validate_call` module caused import errors
Why the fix works: Fix circular import with `validate_call` to resolve issue #10799. (first fixed release: 2.10.0).

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 3.10 in real deployments (not just unit tests).
Circular import in the `validate_call` module caused import errors
Surfaces as: ImportError: cannot import name 'VALIDATE_CALL_SUPPORTED_TYPES' from partially initialized module 'pydantic._internal._validate_call' (most likely due to a circular import)

Proof / Evidence

GitHub issue: #10799
Fix PR: https://github.com/pydantic/pydantic/pull/10807
First fixed release: 2.10.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.53

Discussion

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

Jump to Sources Open on GitHub

“@mayakeeley, Thanks so much for reporting. Are you able to share the code that reproduces this issue with us? We'll investigate before v2.10.0.”

@sydney-runkle · 2024-11-09 · source

“1. Create __init__.py with just the following line: 2. Run it with python __init__.py”

@CyberTailor · 2024-11-10 · source

Failure Signature (Search String)

ImportError: cannot import name 'VALIDATE_CALL_SUPPORTED_TYPES' from partially initialized module 'pydantic._internal._validate_call' (most likely due to a circular import)

Error Message

Stack trace

error.txt

Error Message
-------------
ImportError: cannot import name 'VALIDATE_CALL_SUPPORTED_TYPES' from partially initialized module 'pydantic._internal._validate_call' (most likely due to a circular import)

Minimal Reproduction

repro.py

pydantic version: 2.10.0b1
        pydantic-core version: 2.26.0
          pydantic-core build: profile=release pgo=false
                 install path: /Users/jpdephillips/.local/share/virtualenvs/iconic-DQE3a5P9/lib/python3.10/site-packages/pydantic
               python version: 3.10.0 (default, Mar  8 2024, 14:47:28) [Clang 14.0.0 (clang-1400.0.29.102)]
                     platform: macOS-14.1-x86_64-i386-64bit
             related packages: typing_extensions-4.12.2
                       commit: unknown

Environment

Python: 3.10
Pydantic: 2

What Broke

Users experienced ImportError when trying to import `validate_call`.

Why It Broke

Circular import in the `validate_call` module caused import errors

Fix Options (Details)

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

pip install pydantic==2.10.0

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/10807

First fixed release: 2.10.0

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
2.10.0	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 Circular ref error with `validate_call` (Fix)