FunctionCallOutput is inconsistent with OpenAI API docs

[zhukoff-pavel]

Hello! The FunctionCallOutput in the OpenAPI specification here and in OpenAI documentation seems to be inconsistent:

The current state of that object is as follows (downloaded from https://app.stainless.com/api/spec/documented/openai/openapi.documented.yml at 2025-09-29):

FunctionCallOutputItemParam:
      properties:
        id:
          anyOf:
            - type: string
              description: The unique ID of the function tool call output. Populated when this item is returned via API.
              example: fc_123
            - type: 'null'
        call_id:
          type: string
          maxLength: 64
          minLength: 1
          description: The unique ID of the function tool call generated by the model.
        type:
          type: string
          enum:
            - function_call_output
          description: The type of the function tool call output. Always `function_call_output`.
          default: function_call_output
          x-stainless-const: true
        output:
          anyOf:
            - type: string
              maxLength: 10485760
              description: A JSON string of the output of the function tool call.
        status:
          anyOf:
            - $ref: '#/components/schemas/FunctionCallItemStatus'
              description: >-
                The status of the item. One of `in_progress`, `completed`, or `incomplete`. Populated when
                items are returned via API.
            - type: 'null'
      type: object
      required:
        - call_id
        - type
        - output
      title: Function tool call output
      description: The output of a function tool call.

The output type here is string only, whereas the type listed in the docs is string or array of input contents (image/text/file) (https://platform.openai.com/docs/api-reference/responses/list#responses/list-data-function-tool-call-output-output).