The Fix
pip install pydantic==2.7.1
Based on closed pydantic/pydantic issue #9216 · 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%.
@@ -2,7 +2,9 @@
import dataclasses
-from typing import Callable, Literal
+from typing import Any, Callable, Literal
+
from pydantic import BaseModel, Field, AliasChoices
class FooBase(BaseModel):
foo: str = Field(serialization_alias='bar', validation_alias=AliasChoices('bar', 'foo'))
FooBase.model_construct().dict()
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==2.7.1\nWhen NOT to use: Do not use this fix if the model does not utilize validation_alias with AliasChoices.\n\n
Why This Fix Works in Production
- Trigger: FooBase.model_construct().dict()
- Mechanism: The TypeError occurs due to an unhashable type 'AliasChoices' in the model_construct method
- Why the fix works: Fixes the TypeError in model_construct when using validation_alias with AliasChoices. (first fixed release: 2.7.1).
- 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 3.11 in real deployments (not just unit tests).
- The TypeError occurs due to an unhashable type 'AliasChoices' in the model_construct method
- Surfaces as: Traceback (most recent call last):
Proof / Evidence
- GitHub issue: #9216
- Fix PR: https://github.com/pydantic/pydantic/pull/9223
- First fixed release: 2.7.1
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.75
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.56
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: 2.7.1
- Mode: fixed_only
- Outcome: ok
Logs
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“@twispt, Thanks for reporting this! We'll work on a fix and get a patch release out early next week!”
“I believe this was introduced with https://github.com/pydantic/pydantic/pull/9144”
“Working on a fix now and will have a PR up shortly!”
“I am running into the same issue, and can confirm the code works on v2.6.4 but not on v2.7.0 in v2.6.4 i do not see…”
Failure Signature (Search String)
- FooBase.model_construct().dict()
Error Message
Stack trace
Error Message
-------------
Traceback (most recent call last):
File "/home/bryan/src/temp/pydantic-regression/my.py", line 6, in <module>
FooBase.model_construct().dict()
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/twispt/src/temp/pydantic-regression/.venv/lib/python3.11/site-packages/pydantic/main.py", line 228, in model_construct
elif field.validation_alias is not None and field.validation_alias in values:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unhashable type: 'AliasChoices'
Minimal Reproduction
from pydantic import BaseModel, Field, AliasChoices
class FooBase(BaseModel):
foo: str = Field(serialization_alias='bar', validation_alias=AliasChoices('bar', 'foo'))
FooBase.model_construct().dict()
Environment
- Python: 3.11
- Pydantic: 2
What Broke
Using model_construct results in a TypeError, preventing model instantiation.
Why It Broke
The TypeError occurs due to an unhashable type 'AliasChoices' in the model_construct method
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==2.7.1
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/9223
First fixed release: 2.7.1
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use this fix if the model does not utilize validation_alias with AliasChoices.
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 |
|---|---|
| 2.7.1 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.