Stream API responses with SSE

Set stream: true in a supported generation request. The gateway forwards events incrementally and keeps the selected upstream connection for the life of the stream.

with client.responses.stream(
    model="gpt-5.6-terra",
    input="Write a short welcome message.",
) as stream:
    for event in stream:
        if event.type == "response.output_text.delta":
            print(event.delta, end="", flush=True)

An SSE event ends with a blank line. Network chunks do not necessarily align with events or UTF-8 characters. Use an SDK or an incremental SSE parser rather than treating every received chunk as complete JSON.

• Responses streams use response lifecycle events.
• Chat Completions streams send data events and a [DONE] marker.
• Messages streams use Anthropic event names, including content-block and message lifecycle events.
• A stream can begin successfully and later report an error. Check its completion event and error events.

Closing the client connection cancels the upstream stream. Reported token usage is recorded. If final usage is missing, the charge needs review without reserving your balance; cancellation does not guarantee a free request.

Rolling updates allow existing streams to drain before an instance stops. Network, host or provider failures can still interrupt a connection; applications should handle incomplete output. See HTTP errors and retry guidance and how token usage is charged.