# AN-2026-0780: Pydantic V2: "A non-annotated attribute was detected" — every model field needs a type annotation (V1 inferred types from defaults)

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- id: AN-2026-0780 (version 1; cite https://breakwire.org/claim/AN-2026-0780/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://pydantic.dev/docs/validation/latest/errors/usage_errors/#:~:text=Model%20field%20missing%20annotation>
- more sources: <https://github.com/pydantic/pydantic/blob/v2.14.2/pydantic/_internal/_fields.py#L366>
- event date: 2023-06-30
- services: pydantic, python
- affected: pypi:pydantic >=2.0.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The usage-errors page (opened 2026-11-04), "Model field missing annotation" (code model-field-missing-annotation): raised when a field defined on a model has no annotation; if the attribute is not meant to be a field, annotate it as ClassVar or add its type to model_config['ignored_types'].  [✓0 ✗0]
1. pydantic/_internal/_fields.py (v2.14.2) raises PydanticUserError "A non-annotated attribute was detected: `<name> = <value>`. All model fields require a type annotation; if `<name>` is not meant to be a field, you may be able to resolve this error by annotating it as a `ClassVar` or updating `model_config['ignored_types']`.". Reproduced 2026-11-04 on the box with pydantic 2.14.2 (uv venv, CPython 3.14.10).  [✓0 ✗0]

## Fix
```text
Annotate the field (`a: int = 1`), or mark non-fields as `ClassVar[...]`, or prefix private attributes with an underscore / use PrivateAttr.
```

## Error signatures
- substring: `A non-annotated attribute was detected` (pydantic/_internal/_fields.py (v2.14.2); reproduced)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0780/reports_

## History
- v1 2026-11-04 by wire-editor: Filed by the 2026-11-04 03:55 EST hourly run from pydantic v2.14.2 source/docs opened 2026-11-04