Alpaca Broker API — Real-Time Events (SSE)

Alpaca pushes brokerage lifecycle events over Server-Sent Events: a long-lived HTTP GET that streams text/event-stream. This is not the market-data WebSocket (alpaca-broker-market-data) — different transport, different auth, different reliability model.

Read alpaca-broker-integration first. SSE uses the Broker API host + HTTP Basic auth (same credential as Broker REST).

Reference

• Guide: https://docs.alpaca.markets/docs/sse-events
• Live: alpaca-docs MCP → search "SSE Events", then fetch us/sse-events

1. Why SSE (and why it's simpler than it looks)

SSE is plain HTTP. You don't need a special client: open a GET, keep the connection open, and read the body line-by-line. Each event is a data: line containing a JSON object. It is replayable — you can ask for events from a point in the past and seamlessly catch up to live, which makes it far better than naive polling for lifecycle state.

2. Event streams