# AN-2026-0776: Pydantic 2.14.2 (Oct 29, 2026): model_validate_json now treats keys that only match an unused alias or field name as extra data (extra='forbid' -> extra_forbidden error instead of silently dropped)

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- id: AN-2026-0776 (version 1; cite https://breakwire.org/claim/AN-2026-0776/v/1)
- kind: breaking · status: active · review: editor
- source: <https://github.com/pydantic/pydantic/blob/v2.14.2/HISTORY.md#:~:text=Make%20JSON%20validation%20by%20iteration%20consistent%20with%20Python%20approach>
- more sources: <https://github.com/pydantic/pydantic/pull/13275> <https://pypi.org/project/pydantic/2.14.2/>
- event date: 2026-10-29
- services: pydantic, python
- affected: pypi:pydantic >=2.14.2
- 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. HISTORY.md v2.14.2 (2026-10-29, opened 2026-11-04), Fixes: "Make JSON validation by iteration consistent with Python approach" (#13275) — JSON validation now handles field lookup and extra data the same way as Python validation; keys that only match an unused alias or field name are now treated as extra data instead of being silently dropped.  [✓0 ✗0]
1. Its example: a model with extra='forbid' and alias_generator=to_camel, field page_size; Page.model_validate_json('{"page_size": 50}') returned Page(page_size=10) before and raises ValidationError (extra_forbidden) after. With the default extra='ignore', the snake_case key is still ignored (the field keeps its default).  [✓0 ✗0]
2. Reproduced 2026-11-04: pydantic 2.14.1 returned page_size=10; 2.14.2 raised "Extra inputs are not permitted [type=extra_forbidden, input_value=50, input_type=int]". This shipped in a patch release, so unpinned pydantic>=2.14 installs get it.  [✓0 ✗0]

## Fix
```text
Send the alias (camelCase) keys, or set `validate_by_name=True` (with validate_by_alias) in model_config so field names are accepted, or relax extra='forbid'. Check JSON fixtures that used field names on aliased models; pin pydantic==2.14.1 only as a stopgap.
```

## Outcome reports (0)
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## 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