Inside Stream's Real-Time Architecture for Trading & Investing Apps

Trading and investing apps rely on separate but connected real-time systems: a transaction plane that manages authoritative market data, orders, execution, risk, and ledgers, and an experience plane that distributes alerts, activity feeds, chat, notifications, and video to users. The experience plane must remain responsive during market-open spikes, earnings releases, and major price movements because users often perceive delays in these features as slow trading overall. The piece describes Stream’s proposed architecture for this layer, including hybrid materialized feeds that selectively precompute active users’ timelines while fetching missing updates on demand, edge-based chat with offline-first clients and large-scale message fanout, and cascaded WebRTC SFUs for low-latency video broadcasts and calls. Stream reports benchmark results of roughly 15 ms median feed-read latency for 4.5 million concurrent users, chat delivery supporting a five-million-person channel with average sends below 40 ms, and a 100,000-viewer video stream delivering 225 Gbps with stable 30 fps and no packet loss. It argues that brokerages should retain control of financially sensitive transaction systems while considering specialized infrastructure for the globally distributed, burst-prone user experience features surrounding trading activity.

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