fastapi/docs/en/docs/reference/sse.md

Server-Sent Events - EventSourceResponse and ServerSentEvent

To stream Server-Sent Events (SSE), use yield in your path operation function and set response_class=EventSourceResponse.

If you need to set SSE fields like event, id, retry, or comment, you can yield ServerSentEvent objects instead of plain data.

Read more about it in the FastAPI docs for Server-Sent Events (SSE).

You can import them directly from fastapi.sse:

from fastapi.sse import EventSourceResponse, ServerSentEvent

::: fastapi.sse.EventSourceResponse

::: fastapi.sse.ServerSentEvent