Pydantic Type of "Field" is partially unknown after v2.10

The Fix

pip install pydantic==2.10.2

Based on closed pydantic/pydantic issue #10971 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -734,7 +734,7 @@ class _EmptyKwargs(typing_extensions.TypedDict):
 @overload  # type hint the return value as `Any` to avoid type checking regressions when using `...`.
 def Field(
-    default: _typing_extra.EllipsisType,
+    default: ellipsis,  # noqa: F821  # TODO: use `_typing_extra.EllipsisType` when we drop Py3.9
     *,

repro.py

# pyproject.toml
[tool.pyright]
typeCheckingMode = "strict"
pythonVersion = "3.8"

reportUnusedImport = false

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==2.10.2\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: After `v2.10` Pyright will report an error that `Field` is partially unknown. Note that I'm unsure if this is an issue with Pydantic or Pyright.
Mechanism: Fix type hint of `Field.default` to be compatible with Python 3.8 and 3.9, resolving the issue where Pyright reports that `Field` is partially unknown after v2.10.
Why the fix works: Fix type hint of `Field.default` to be compatible with Python 3.8 and 3.9, resolving the issue where Pyright reports that `Field` is partially unknown after v2.10. (first fixed release: 2.10.2).

Why This Breaks in Prod

Shows up under Python 3.9 in real deployments (not just unit tests).
Production symptom (often without a traceback): After `v2.10` Pyright will report an error that `Field` is partially unknown. Note that I'm unsure if this is an issue with Pydantic or Pyright.

Proof / Evidence

GitHub issue: #10971
Fix PR: https://github.com/pydantic/pydantic/pull/10972
First fixed release: 2.10.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.64

Discussion

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

Jump to Sources Open on GitHub

“### Initial Checks - [X] I confirm that I'm using Pydantic V2 ### Description After v2.10 Pyright will report an error that Field is partially unknown. Note that I'm unsure if this is an issue with Pydantic or Pyright. with Pyright will rep”

Issue thread · issue description · source

Failure Signature (Search String)

After `v2.10` Pyright will report an error that `Field` is partially unknown. Note that I'm unsure if this is an issue with Pydantic or Pyright.
pd1/main.py:1:22 - error: Type of "Field" is partially unknown

Copy-friendly signature

signature.txt

Failure Signature
-----------------
After `v2.10` Pyright will report an error that `Field` is partially unknown. Note that I'm unsure if this is an issue with Pydantic or Pyright.
pd1/main.py:1:22 - error: Type of "Field" is partially unknown

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
After `v2.10` Pyright will report an error that `Field` is partially unknown. Note that I'm unsure if this is an issue with Pydantic or Pyright.
pd1/main.py:1:22 - error: Type of "Field" is partially unknown

Minimal Reproduction

repro.py

# pyproject.toml
[tool.pyright]
typeCheckingMode = "strict"
pythonVersion = "3.8"

reportUnusedImport = false

Environment

Python: 3.9
Pydantic: 2

What Broke

Pyright reports that `Field` is partially unknown, causing type checking failures.

Fix Options (Details)

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

pip install pydantic==2.10.2

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/10972

First fixed release: 2.10.2

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
2.10.2	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:serialization Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Configuration error Data consistency OpenAPI schema

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Pydantic Type of "Field" is partially unknown after v2.10 (Fix)