The Fix
pip install pydantic==2.9.1
Based on closed pydantic/pydantic issue #10319 · 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%.
@@ -319,6 +319,8 @@ def val_func(v: Any) -> Any:
)
+ return v
+
schema = cs.no_info_after_validator_function(val_func, schema)
repro.py
from typing import TypeAlias
from typing import Annotated
from annotated_types import Predicate
from pydantic import BaseModel
def is_positive(value: int) -> bool:
return value > 0
PositiveInt: TypeAlias = Annotated[int, Predicate(is_positive)]
class MyModel(BaseModel):
foo: PositiveInt
m = MyModel.model_validate({'foo': 3})
assert m.foo == 3
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==2.9.1\nWhen NOT to use: Do not use this fix if you require the previous behavior of `Predicate`.\n\n
Why This Fix Works in Production
- Trigger: Using `annotated_types.Predicate` gives unexpected result in 2.9.0. The below code fails but works in <2.9.0. Also replacing `PositiveInt` with `Annotated[int,…
- Mechanism: Fixes an issue with `Predicate` in Pydantic v2.9.0 that caused unexpected results.
- Why the fix works: Fixes an issue with `Predicate` in Pydantic v2.9.0 that caused unexpected results. (first fixed release: 2.9.1).
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 in real deployments (not just unit tests).
- Production symptom (often without a traceback): Using `annotated_types.Predicate` gives unexpected result in 2.9.0. The below code fails but works in <2.9.0. Also replacing `PositiveInt` with `Annotated[int, Gt(0)]` (with `Gt` also from `annotated_types`) does work in 2.9.0.
Proof / Evidence
- GitHub issue: #10319
- Fix PR: https://github.com/pydantic/pydantic/pull/10321
- First fixed release: 2.9.1
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.58
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“@AckslD, Thanks for reporting this. Indeed, a bug on our end. I've opened https://github.com/pydantic/pydantic/pull/10321 to fix this issue, and we'll roll out the fix in…”
Failure Signature (Search String)
- Using `annotated_types.Predicate` gives unexpected result in 2.9.0. The below code fails but works in <2.9.0. Also replacing `PositiveInt` with `Annotated[int, Gt(0)]` (with `Gt`
- assert m.foo == 3
Copy-friendly signature
signature.txt
Failure Signature
-----------------
Using `annotated_types.Predicate` gives unexpected result in 2.9.0. The below code fails but works in <2.9.0. Also replacing `PositiveInt` with `Annotated[int, Gt(0)]` (with `Gt` also from `annotated_types`) does work in 2.9.0.
assert m.foo == 3
Error Message
Signature-only (no traceback captured)
error.txt
Error Message
-------------
Using `annotated_types.Predicate` gives unexpected result in 2.9.0. The below code fails but works in <2.9.0. Also replacing `PositiveInt` with `Annotated[int, Gt(0)]` (with `Gt` also from `annotated_types`) does work in 2.9.0.
assert m.foo == 3
Minimal Reproduction
repro.py
from typing import TypeAlias
from typing import Annotated
from annotated_types import Predicate
from pydantic import BaseModel
def is_positive(value: int) -> bool:
return value > 0
PositiveInt: TypeAlias = Annotated[int, Predicate(is_positive)]
class MyModel(BaseModel):
foo: PositiveInt
m = MyModel.model_validate({'foo': 3})
assert m.foo == 3
Environment
- Python: 3.12
- Pydantic: 2
What Broke
Users experienced validation failures when using `Predicate` with `Annotated` types.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==2.9.1
When NOT to use: Do not use this fix if you require the previous behavior of `Predicate`.
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/10321
First fixed release: 2.9.1
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use this fix if you require the previous behavior of `Predicate`.
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 |
|---|---|
| 2.9.1 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.