Latency arbitrage: what it is and isn't

[Fairman]

Latency arbitrage: what it is and isn't

Latency arbitrage exploits the delay between price updates at different venues or brokers. A fast participant sees a price change at one place before another updates, and trades against the stale quote.

At the institutional level, it's a competition in microseconds. Retail brokers are the slow quote, and professionals who target them are called toxic flow by the brokers.

Retail traders sometimes try the same trick: watching a fast feed and trading on a slow broker. In practice, the slow broker has defenses. Last look, delay on execution, minimum hold times, and quick account restrictions all protect against it.

The strategy also has a short life. Brokers who detect the pattern change terms or close accounts.

For ordinary scalpers, the relevance is indirect. Broker policies designed to stop latency arbitrage affect everyone. Execution delays and rejections that appear arbitrary may be defenses aimed at someone else.

A scalper whose strategy is based on market behavior, not on feed delays, is generally safe. But the line isn't always clear, and brokers are rarely transparent about where it sits.

Reading the policy and asking support directly is the best protection.

A neutral way to test whether a strategy is likely to be treated as toxic is to look at its markouts. Toxic flow is typically trades that systematically move in the trader's favor right after the fill, within a second or two. A strategy with persistently large positive markouts at very short horizons looks like latency exploitation to a broker's risk engine, even if the intent was entirely different.

That doesn't prove a problem. But it's the metric that brokers watch, and knowing the number lets a trader anticipate how the strategy might be viewed. A strategy whose profits come from holding periods of minutes or more shows little short-horizon markout and is rarely troubled.

Latency-sensitive strategies: what did the broker's policy say, and how was it clarified?