Problem

When using ->asJsonResponse($schema) with the Anthropic provider, the API returns errors:

Bad Request (400) - response_format.json_schema.name: Field required
# Added `name` field to schema wrapper, then got:

Bad Request (400) - response_format.json_schema.strict: Field required
# Added `strict: true` to schema wrapper, then got:

Bad Request (400) - output_config: Extra inputs are not permitted
# Anthropic doesn't recognize `response_format` at all—it's an OpenAI parameter

The library sends OpenAI's response_format parameter to Anthropic's API, which now rejects it. This appears to have started around December 4, 2025 when Anthropic launched their structured outputs feature—prior to this, the parameter was likely ignored.

Proposed Solution

Anthropic's structured outputs use a different format than OpenAI:

The Anthropic provider should override prepareGenerateTextParams() to:

1. Use output_format instead of response_format
2. Add the required beta header

References

• Anthropic Structured Outputs Documentation
• Anthropic API Release Notes