No Streaming Response for Application Load Balancer + Lambda (Fastapi : server sent event -> streaming response)

[GxWwT]

from fastapi.responses import StreamingResponse

if chat_request.stream:
    return StreamingResponse(
        content=model.chat_stream(chat_request), media_type="text/event-stream"
    )

This approach, when redirected to ALB through Mangum, loses the streaming response. Instead, all chunks are printed out all at once.