Pydantic Type alias for model_dump include/exclude is

The Fix

pip install pydantic==2.9.1

Based on closed pydantic/pydantic issue #10333 · 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

@@ -5,7 +5,7 @@
 strategy = []
 lock_version = "4.5.0"
-content_hash = "sha256:3a584a7e92099980d8871eb23c5549630f86f8e2284884ab3042dd043ddf50f8"
+content_hash = "sha256:353e0a512023413e67aad3b741688cdb4c38fe003b8ce6cc28f9f0271d9d7d0a"

repro.py

from pydantic import BaseModel

class ExampleModel(BaseModel):
    example_field: str
    field_to_be_excluded: str

e = ExampleModel(example_field="Hello Pydantic", field_to_be_excluded="To be excluded")
e.model_dump(exclude={"field_to_be_excluded": True}) # mypy complains about this

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 rely on the previous behavior of `IncEx` type alias.\n\n

Why This Fix Works in Production

Trigger: from pydantic import BaseModel
Mechanism: The `IncEx` type alias was incorrectly defined, causing type errors in the `model_dump` method
Why the fix works: Fixes the `IncEx` type alias definition, addressing issues with the include/exclude parameters in the model_dump method. (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).
The `IncEx` type alias was incorrectly defined, causing type errors in the `model_dump` method
Surfaces as: from pydantic import BaseModel

Proof / Evidence

GitHub issue: #10333
Fix PR: https://github.com/pydantic/pydantic/pull/10339
First fixed release: 2.9.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.51

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: 2.9.1
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

Discussion

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

Jump to Sources Open on GitHub

“@tommasolevato, Thanks for reporting. Indeed, looks like an issue in v2.9.0, we'll work to roll out a fix shortly.”

@sydney-runkle · 2024-09-06 · source

“Yes, ref: https://docs.pydantic.dev/latest/concepts/serialization/#advanced-include-and-exclude”

@tommasolevato · 2024-09-10 · source

“I've found another problem with IncEx, that v2.9.1 did not address: I wasn't sure if it was appropriate to open another issue, so I decided…”

@tommasolevato · 2024-09-10 · source

“Did you mean to write: ? Afaik dict[str, str] isn't supported.”

@Viicos · 2024-09-10 · source

Failure Signature (Search String)

from pydantic import BaseModel

Error Message

Stack trace

error.txt

Error Message
-------------
from pydantic import BaseModel

class ExampleModel(BaseModel):
    example_field: str
    field_to_be_excluded: str

e = ExampleModel(example_field="Hello Pydantic", field_to_be_excluded="To be excluded")
e.model_dump(exclude={"field_to_be_excluded": True}) # mypy complains about this

Stack trace

error.txt

Error Message
-------------
class ExampleElement(BaseModel):
    number: int
    name: str


class ExampleModel(BaseModel):
    elements: list[ExampleElement]


e = ExampleModel(elements=[ExampleElement(number=1, name="Hello Pydantic")])
e.model_dump(exclude={"elements": {"_all": "number"}})  # mypy complains about this

Minimal Reproduction

repro.py

from pydantic import BaseModel

class ExampleModel(BaseModel):
    example_field: str
    field_to_be_excluded: str

e = ExampleModel(example_field="Hello Pydantic", field_to_be_excluded="To be excluded")
e.model_dump(exclude={"field_to_be_excluded": True}) # mypy complains about this

Environment

Python: 3.12
Pydantic: 2

What Broke

Users experienced type errors when using `include` and `exclude` parameters in `model_dump`.

Why It Broke

The `IncEx` type alias was incorrectly defined, causing type errors in the `model_dump` method

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 rely on the previous behavior of `IncEx` type alias.

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/10339

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 rely on the previous behavior of `IncEx` type alias.

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	Broken
2.9.1	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 Type alias for model_dump include/exclude is broken (Fix)