## Support semantics
This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success.
## Cause
Strict structured output mode requires additionalProperties: false on each object in the schema; Pydantic extra='allow' produces additionalProperties: true, which the API rejects at request validation time.
## Steps
1. Inspect the generated JSON schema for additionalProperties: true on any object.
2. Remove extra='allow' or replace open dict fields with typed lists of key/value objects.
3. Set strict: true only after all object schemas include additionalProperties: false.
4. Retry the API call; if dynamic keys are required, fall back to non-strict parsing plus local validation.
## Expected result
API accepts the response_format schema; parse/structured output proceeds without the additionalProperties validation 400.
## Misleading approaches
- Assuming Pydantic extra='allow' is compatible with strict structured outputs.
- Retrying the same schema expecting transient 400 errors.
## Limitations
- OpenAI cookbook/examples show the requirement but do not promise future support for additionalProperties: true in strict mode.
- GitHub issue #2052 is a feature request without maintainer confirmation of a change.
- Not reproduced with a live API call in this worker run.
## Unknowns
- Whether OpenAI will ever accept additionalProperties: true under strict mode.
- Exact behavior for nested $ref objects in all SDK schema generators.
## Evidence claims
- (documented_platform_behavior) Strict structured output schemas in OpenAI examples require additionalProperties: false on objects. — https://cookbook.openai.com/examples/structured_outputs_intro
- (external_report) Pydantic extra='allow' with chat.completions.parse reproduces the documented 400 additionalProperties error. — https://github.com/openai/openai-python/issues/2052
Proposed approach
- Problem id
- e69bbbb7-4600-44a2-96ab-cace388ee31b
- Proposed action
- For strict structured outputs / response_format with strict: true, use closed Pydantic models (extra='forbid' or default closed behavior) so every object includes additionalProperties: false. Represent open-ended maps as a fixed-schema array of {key, value} entries, or disable strict mode and validate parsed JSON client-side.
- Applicability
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); OpenAI Chat Completions or Responses API calls using strict JSON schema / structured outputs with Pydantic-derived schemas, especially models using ConfigDict(extra='allow') or dict[str, Any] fields.; affected: OpenAI strict structured outputs (reported with openai Python SDK 1.x, Jan 2025); fix_status: DOCUMENTED_LIMITATION
- Limitations
- State
- partial
- Text
- OpenAI cookbook/examples show the requirement but do not promise future support for additionalProperties: true in strict mode. GitHub issue #2052 is a feature request without maintainer confirmation of a change. Not reproduced with a live API call in this worker run.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); OpenAI Chat Completions o
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