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

| Stream | Path | Carries | |--------|------|---------| | Account status | GET /v1/events/accounts/status | Account-property changes: status/crypto_status (SUBMITTED→ACTIVE, ACTION_REQUIRED, REJECTED), plus kyc_results, account_blocked, trading_blocked, cash_interest, options | | Journal status | GET /v2/events/journals/status | JNLC/JNLS lifecycle (queued→executed, correct…) | | Funding/transfer status | GET /v2/events/funding/status | Unified: Transfer, BankRelationship, WireBank, FundingWallet entities (switch on entity_type) | | Trade updates | GET /v2/events/trades | Order events in the event field: new, fill, partial_fill, canceled, rejected, held, trade_bust, trade_correct… (richer than order status) | | Non-trade activities | GET /v1/events/nta | Dividends, interest, fees, splits, ACATs, cash disbursements. entry_type e.g. JNLC/FEE/INT/DIVNRA/CSD; status ∈ executed/correct/canceled |

> Paths & versions are NOT uniform — verify each. This is exactly the kind of cross-stream inconsistency Alpaca's docs under-communicate: > - /v2 streams (trades, journals/status, funding/status) use a ULID event_id directly; /v1/events/trades and /v1/events/journals/status are legacy (existing partners only — migrate to v2). /v2/events/trades was previously /v2beta1, now redirected. > - /v1 streams (accounts/status, nta) are current, not deprecated — there is no v2 yet. Each event carries both an integer event_id and a ULID event_ulid. > > Every event carries at (timestamp), account_id, and status_from/status_to (account/journal/funding) or event+order (trades).

3. Connection

GET /v2/events/journals/status?since_id=<last-ulid-you-saw> HTTP/1.1
Host: broker-api.alpaca.markets
Authorization: Basic <base64(key:secret)>
Accept: text/event-stream

Read the response stream and parse data: {…} frames as they arrive. In most languages an off-the-shelf EventSource/SSE client works — just make sure it lets you set the Authorization header on the initial request (the browser EventSource API famously does not; use a server-side SSE library instead).

4. Replay cursors — the feature that prevents data loss

Every stream supports point-in-time replay:

| Param | Meaning | |-------|---------| | since / until | Date or RFC3339 timestamps. URL-encode + in offsets as %2B. | | since_id / until_id | ID cursors. On v2 streams the ID is a ULID. On v1 streams it's the integer event_id. | | since_ulid / until_ulid | v1 streams only (accounts, nta) — ULID-based cursors, since v1 events carry both an int event_id and a event_ulid. |

Rules: since is required if until is set; since_id required if until_id set (same for since_ulid/until_ulid); you can't mix since, since_id, and since_ulid. Without any since cursor, no history is returned — you only get live pushes from now on. Reaching the until bound ends the stream with a 200.

This is the single most important reliability lesson: persist the ID of the last event you successfully processed. On every (re)connect, pass it as your since cursor (since_id on v2; since_ulid or since_id on v1) so Alpaca replays anything you missed during the gap. A consumer that reconnects without a cursor silently drops every event that occurred while it was down.

5. Ordering caveat

Within a millisecond, ULIDs contain a random component, so two events in the same millisecond can sort either way. Alpaca's own guidance: for reconciliation, restart the stream from a since a few minutes before your last event and rely on idempotent processing to absorb the overlap. Don't assume strict total ordering — assume approximate ordering plus dedup.

6. Reliability patterns (hard-won)

SSE connections drop — networks, load balancers, deploys, and Alpaca-side resets all happen. A production consumer needs:

1. Heartbeat / silence detection. SSE has no application heartbeat by default. Track lastMessageAt on every frame; if the stream is silent past a threshold (e.g. 5 min), proactively tear down and reconnect — a dead socket often looks "open."
2. Reconnect with exponential backoff + cap. On error/close, reconnect after a delay that doubles up to a ceiling (e.g. start 1s, cap 60s). Reset the delay on a successful connect.
3. A single-reconnect guard. Use a flag so an error storm doesn't spawn many concurrent reconnect attempts racing each other.
4. Always reconnect with since_id = last processed event (see §4).
5. Process idempotently (see §7) — overlap from replay is expected, not exceptional.
6. Don't let a side-effect failure kill the stream. Wrap per-event processing in try/catch; log and continue. One bad event (or a downstream outage) must not stop you consuming the rest.

> Note: OpenAPI can't fully model SSE, so generated API clients often hang on these endpoints (waiting for a response that never ends). Use a real streaming HTTP/SSE client, not a codegen'd one.

7. Idempotent processing pipeline

The robust shape for each event:

parse → persist a raw event snapshot (keyed on event_id, skip-if-exists)
      → match the local record by Alpaca ID (account_id / journal_id / order_id / transfer_id)
      → update local state under a row lock / guarded by current status
      → fire side effects (notifications, downstream transfers)
      → advance the stored cursor to this event_id

• Snapshot-first, keyed on event_id. Insert the raw event with an upsert/skip-duplicate on event_id. A duplicate (from replay or an at-least-once redelivery) is then a no-op. This is your dedup boundary.
• Lock the target row (SELECT … FOR UPDATE or equivalent) when mutating a transfer/order so two events for the same record can't race.
• Guard transitions by current status — e.g. only act on a transfer that isn't already in a terminal state, so a late/duplicate "executed" doesn't re-trigger a payout.
• Advance the cursor only after successful processing, so a crash mid-event replays it rather than skipping it (at-least-once, which idempotency makes safe).

8. Per-stream notes

• Account status: drive onboarding UI and "enable trading" off status_to == ACTIVE. Reject sandbox/paper account IDs in live handlers.
• Trade updates: new/accepted/pending_new are pre-fill; update local order state on fill/partial_fill/canceled/rejected. Invalidate any cached portfolio/holdings on fills.
• Journals: remember executed isn't final and correct spawns a new journal ID (see alpaca-broker-journals). Idempotency + ID-keyed snapshots absorb both.
• Funding/transfer: unified stream across 4 entity types; switch on entity_type. Funding-wallet per-transfer status may still need polling (alpaca-broker-funding-transfers).
• NTA: dividends/fees/interest/corporate-actions — persist as activity snapshots; these feed balance/portfolio reconciliation.

9. SSE is necessary but not sufficient

Even a perfect consumer can miss events (extended downtime beyond retention, a bug, an un-handled type). Always pair SSE with a periodic reconciliation/heal pass that re-pulls authoritative state (activities, journals, transfers) from Alpaca and upserts it. SSE is for low latency; reconciliation is for correctness. See alpaca-broker-reconciliation-idempotency.

Related skills: correctness backstop → alpaca-broker-reconciliation-idempotency; dedup/idempotency mechanics → alpaca-broker-reconciliation-idempotency; backoff details → alpaca-broker-rate-limits-resilience; market-data streaming (WS, not SSE) → alpaca-broker-market-data.