The content of the output message.
A text output from the model.
The annotations of the text output.
A citation for a web resource used to generate a model response.
The status of the message input. One of in_progress, completed, or
incomplete. Populated when input items are returned via API.
Labels an assistant message as intermediate commentary (commentary) or the final answer (final_answer).
For models like gpt-5.3-codex and beyond, when sending follow-up requests, preserve and resend
phase on all assistant messages — dropping it can degrade performance. Not used for user messages.