Susquehanna International Group, one of the largest options trading firms on the planet, is claiming it got fleeced. The firm has filed a lawsuit in Manhattan federal court alleging that anonymous traders used insider knowledge of an impending Chinese regulatory crackdown to rake in more than $100 million in options profits, leaving SIG holding the bag for over $70 million in losses.

The case names 100 John Doe defendants, which is legal speak for “we know someone did this, we just don’t know who yet.” And SIG is pulling every lever it can to find out.

What actually happened

On May 22, 2026, the Chinese government dropped a regulatory hammer on cross-border brokerages. New rules targeting firms operating across borders sent shockwaves through the sector.

According to SIG’s complaint, unidentified traders purchased roughly $12 million worth of options linked to Chinese securities firms shortly before the crackdown was announced. Those positions, which primarily consisted of put options (bets that prices would fall), exploded in value once the news broke.

The result: over $100 million in profits from a $12 million outlay. SIG, which sat on the other side of many of these trades as a market maker, watched $70 million evaporate.

The securities at the center of the alleged scheme include Futu Holdings and Up Fintech (commonly known as Tiger Brokers), both of which are Chinese fintech companies with US-listed shares that would have been directly impacted by Beijing’s regulatory moves.

The hunt for the traders

SIG has taken the unusual step of filing a civil lawsuit on its own, rather than relying solely on government enforcement agencies to build a case. SIG has already secured court orders freezing accounts linked to the suspected traders. The firm is also pursuing subpoenas against several brokerage platforms, including Interactive Brokers and Futu, to unmask the identities behind the trades.

Both the SEC and the Department of Justice are reportedly investigating the allegations as well, though neither agency has announced formal charges. The details of those probes remain confidential for now.

The Citadel connection (or lack thereof)

Early reporting linked Citadel Securities to this case, with some outlets suggesting the market-making giant was a victim of the same scheme. However, deeper examination of the situation suggests this may be a misattribution. Citadel Securities does not appear to have been implicated as either a party to the trades or an affected counterparty in the lawsuit SIG has filed.

Citadel Securities and Susquehanna are two of the most dominant options market makers in the world. The distinction matters because it changes the scope of the story. As it stands, SIG appears to be the primary firm claiming damages.

Why this matters for markets

This case is particularly notable because of the geopolitical dimension. The insider information in question wasn’t about a company’s earnings or a merger. It was about a sovereign government’s regulatory decision, putting it in a category where the source of the leak could be a government official, a regulatory insider, or someone in the advisory chain between Beijing and the affected companies.

If federal prosecutors eventually bring criminal charges, this case could become one of the larger insider trading prosecutions in recent memory, both in dollar terms and in its cross-border complexity. The SEC and DOJ investigations add another layer of uncertainty, though details of those probes remain confidential.