MessageDeltaContentTextObject(Text)

{
    "index": 0,
    "type": "text",
    "text": {
        "value": "string",
        "annotations": [
            {
                "index": 0,
                "type": "file_citation",
                "text": "string",
                "file_citation": {
                    "file_id": "string",
                    "quote": "string"
                },
                "start_index": 0,
                "end_index": 0
            }
        ]
    }
}