Short answer: you’re right — it controls live event streaming to clients (including the UI). Turning it off disables real-time updates over WebSockets; everything else keeps working. Details (Prefect 3.x): - What it does: Toggles the Event Distributor service that streams events to subscribers over the

/api/events/out

WebSocket. - If you turn it off: - You lose real-time UI updates (the UI will rely on polling/refresh). - Any custom clients listening to

/api/events/out

won’t receive live events. They’ll only get the initial backfill of recent events, then silence. - What still works: - Event ingestion and persistence to the database - Event querying via REST - Automations and triggers (reactive and proactive) - Webhooks and actions - Flow runs and all server-side processing Related note: This setting is for events only. Log streaming has its own toggle:

PREFECT_SERVER_LOGS_STREAM_OUT_ENABLED

. Useful links: - Settings reference: stream_out_enabled - WebSocket endpoint: /api/events/out handler - Distributor service code: Distributor service - Settings model (env var aliases): server.events settings