IEX Group clears path for new options exchange after court ruling against Citadel Securities

The company that inspired Michael Lewis’s Flash Boys just won another round against one of Wall Street’s most powerful trading firms. A federal appeals court has rejected Citadel Securities’ challenge to IEX’s new options exchange, clearing the way for a launch that could reshape how options are traded in the US.

The US Court of Appeals for the Eleventh Circuit ruled on May 29 against Citadel Securities, upholding the SEC’s approval of IEX Options. That approval had been granted on September 18, 2025, but Citadel filed a petition with the court just a month later, on October 17, effectively putting IEX’s plans in legal limbo.

That limbo is now over. IEX Group is targeting an October 2, 2026 launch date for the new exchange.

The 350-microsecond fight

At the heart of this legal battle is something called the Options Risk Parameter, or ORP. It’s a hardware-based feature that introduces a 350-microsecond delay into the trading process. To put that in perspective, 350 microseconds is about one-third of a millisecond. A blink of an eye takes roughly 300,000 microseconds.

In English: it’s an almost imperceptibly tiny pause designed to protect liquidity providers, the firms that post buy and sell orders on an exchange, from being picked off by faster traders using latency arbitrage. Latency arbitrage is the practice of exploiting tiny speed advantages to trade ahead of others, essentially profiting from being a few microseconds faster than everyone else.

IEX has been fighting this particular war for years. The company’s equities platform won approval for a similar “speed bump” mechanism back in 2022. Citadel challenged that one too. Citadel lost that one too.

Citadel Securities, led by Ken Griffin, has consistently argued that IEX’s delay mechanisms are anticompetitive. The court, for the second time, disagreed. Better Markets, a nonprofit that advocates for stronger financial regulation, filed an amicus brief supporting IEX and highlighting the potential benefits for retail investors.

Why IEX’s options exchange matters

IEX Options is designed around two key principles. First, it prioritizes customer orders. Second, it uses a pro-rata allocation model, meaning orders are filled proportionally rather than on a strict first-come, first-served basis that rewards the fastest connections.

IEX was founded by Brad Katsuyama, who became a household name (at least in finance households) after Lewis’s 2014 book exposed how high-frequency traders were effectively front-running ordinary investors. The company initially announced plans for the options venue in 2024, with an original target of launching by the end of Q1 2026. The Citadel lawsuit pushed that timeline back, but not by much.

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