What Does Real-Time Market Data Mean?
Real-time describes data delivered with little delay under a particular feed and entitlement; it is not a universal guarantee.
Read the draftReal-Time Market Data
IEX vs. SIP Market Data
IEX data reflects one U.S. exchange. SIP data consolidates specified trade and quote reports across U.S. exchanges. The difference is coverage, not simply whether a number is marked live.
Draft updated · owner review pending
One venue versus consolidated reporting
Alpaca's documentation identifies its IEX stream as exchange-specific and its SIP stream as consolidated. A stock may trade on another venue while no new IEX trade arrives, so the latest IEX print and consolidated last trade can differ.
Entitlements change what you receive
Alpaca's plan and feed rules control access to recent SIP data. The provider also describes delayed SIP. Do not assume a paid software license grants exchange data rights; check the data plan tied to the customer's own Alpaca account.
Compare like with like
When diagnosing two platforms, record symbol, timestamp, session, field (bid, ask, or last), and feed. A quote should be compared with a quote from the same moment—not with a trade print from a different source.
Sources and further reading
- Alpaca Market Data FAQFeed coverage, entitlements, and recent historical data
- Alpaca Real-time Stock DataStock stream messages, feed types, and delayed SIP