Short answerIf your rebuilt assistant must return data for another system, use structured outputs: you give a JSON schema and the model's reply conforms to it. OpenAI and Anthropic both document this.
- OpenAI: set text.format to json_schema with strict true in the Responses API. Plain JSON mode only guarantees valid JSON, while structured outputs enforce your schema.
- Anthropic: add an output_config format of type json_schema with your schema; it uses constrained decoding and needs no beta header. An older output_format parameter is deprecated.
When you need it
When a GPT Action returned data to your system or when the replacement fills a form, creates records or feeds a workflow. Pair it with tool definitions: schema mapping and MCP. Developers can plan the rebuild with the architecture overview.
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Sources
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