The Fix
pip install pydantic==2.10.0
Based on closed pydantic/pydantic issue #10780 · 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%.
@@ -60,6 +60,7 @@ def origin_is_union(tp: type[Any] | None) -> bool:
EllipsisType = type(Ellipsis)
else:
+ from types import EllipsisType as EllipsisType
from types import NoneType as NoneType
from pydantic import BaseModel, Field
class Foobar(BaseModel):
x: int = Field(..., description="The X value")
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
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: 2.10 breaks type checking for `Field(...)`
- Why the fix works: the upstream fix ships in 2.10.0.
- 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 in real deployments (not just unit tests).
- Production symptom (often without a traceback): 2.10 breaks type checking for `Field(...)`
Proof / Evidence
- GitHub issue: #10780
- Fix PR: https://github.com/pydantic/pydantic/pull/10781
- First fixed release: 2.10.0
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.70
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.66
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: 2.10.0
- Mode: fixed_only
- Outcome: ok
Logs
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“I'm guessing https://github.com/pydantic/pydantic/pull/10661 is related”
Failure Signature (Search String)
- 2.10 breaks type checking for `Field(...)`
- As of 2.10, it fails with:
Copy-friendly signature
Failure Signature
-----------------
2.10 breaks type checking for `Field(...)`
As of 2.10, it fails with:
Error Message
Signature-only (no traceback captured)
Error Message
-------------
2.10 breaks type checking for `Field(...)`
As of 2.10, it fails with:
Minimal Reproduction
from pydantic import BaseModel, Field
class Foobar(BaseModel):
x: int = Field(..., description="The X value")
Environment
- Python: 3.12
- Pydantic: 2
What Broke
Type checking errors occurred, preventing successful validation of models using Field(...).
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==2.10.0
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/10781
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
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.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.