Summary
The Anthropic-to-Responses translation added in #5901 can emit strict: true for an incomplete object schema such as { "type": "object" }.
Reproduction
Send an Anthropic Messages request with:
{
"output_config": {
"format": {
"type": "json_schema",
"schema": { "type": "object" }
}
}
}isAnthropicOutputSchema accepts this because its compatibility probe normalizes a clone. satisfiesOpenAiStrictSchema then sees no existing properties map to inspect, returns true, and formatFromOutputConfig forwards the unchanged schema with strict: true.
Impact
The translated Responses request claims strict compatibility but lacks the required object closure and required-field contract, so a conforming OpenAI Structured Outputs endpoint can reject it instead of applying the intended best-effort fallback.
Official OpenAI documentation requires the root to be an object, every object to use additionalProperties: false, and every declared field to be required. Unsupported composition must not be marked strict: https://developers.openai.com/api/docs/guides/structured-outputs#supported-schemas
Expected behavior
- Evaluate the original forwarded schema, not the normalized Anthropic acceptance clone.
- Emit
strict: false for bare, open, malformed, optional-field, root-union, or unsupported-composition schemas.
- Preserve valid closed schemas, nested objects, arrays, definitions, and caller schema identity.
- Do not rewrite optional fields or silently close the caller's schema.
Regression coverage
Cover the helper, Anthropic inbound translation, and the parsed Responses request, including recursive nested schemas and literal/property names that resemble schema keywords.
Summary
The Anthropic-to-Responses translation added in #5901 can emit
strict: truefor an incomplete object schema such as{ "type": "object" }.Reproduction
Send an Anthropic Messages request with:
{ "output_config": { "format": { "type": "json_schema", "schema": { "type": "object" } } } }isAnthropicOutputSchemaaccepts this because its compatibility probe normalizes a clone.satisfiesOpenAiStrictSchemathen sees no existingpropertiesmap to inspect, returns true, andformatFromOutputConfigforwards the unchanged schema withstrict: true.Impact
The translated Responses request claims strict compatibility but lacks the required object closure and required-field contract, so a conforming OpenAI Structured Outputs endpoint can reject it instead of applying the intended best-effort fallback.
Official OpenAI documentation requires the root to be an object, every object to use
additionalProperties: false, and every declared field to be required. Unsupported composition must not be marked strict: https://developers.openai.com/api/docs/guides/structured-outputs#supported-schemasExpected behavior
strict: falsefor bare, open, malformed, optional-field, root-union, or unsupported-composition schemas.Regression coverage
Cover the helper, Anthropic inbound translation, and the parsed Responses request, including recursive nested schemas and literal/property names that resemble schema keywords.