Citadel: The Firm That Bought a $45 Billion Portfolio in a Single Trade
When Leopold Aschenbrenner’s fund collapsed last week, one firm stepped in and acquired the entire portfolio in a single block trade. Here is how Citadel operates, and why it was uniquely positioned to do it.
On July 30, 2026, Goldman Sachs, JPMorgan Chase, and Bank of America issued margin calls on Situational Awareness, Leopold Aschenbrenner’s AI hedge fund. The fund needed to sell its entire public book immediately. The buyer, acquiring tens of billions in AI stocks in a single block trade at distressed prices, was Citadel.
The buyer, acquiring tens of billions in AI stocks in a single block trade at distressed prices, was Citadel. What that trade reveals about how the firm operates is worth understanding.
Citadel runs two separate businesses that share a name, a founder, and a building in Miami, but operate in fundamentally different ways.
Citadel: The Firm That Bought a $45 Billion Portfolio in a Single Trade //Peiid
Ken Griffin and the Origin
Kenneth Griffin founded Citadel in 1990 with $4.6 million, raised partly from family and friends. He was 22. He had started trading convertible bonds from his Harvard dormitory two years earlier, reportedly installing a satellite dish on the roof to get real-time price data.
Thirty-six years later, Citadel is the most profitable hedge fund in history. Since inception, it has generated $83 billion in net gains for investors, more than any other hedge fund on record. Griffin himself has a net worth of approximately $27 billion. The firm manages around $69 billion in assets as of mid-2026.
Citadel the Hedge Fund
The hedge fund side of the business, formally called Citadel LLC, runs a multi-strategy approach. Rather than making one large directional bet on markets, it employs hundreds of portfolio managers running independent strategies across equities, fixed income, macro, commodities, and quantitative trading simultaneously. The idea is that diversification across strategies reduces the reliance on any single call being right.
The flagship Wellington fund gained 10.2% in 2025, a solid but not extraordinary year by its own historical standards. In 2022, a year when most funds lost money and global markets fell sharply, Citadel’s hedge fund generated approximately $28 billion in revenue, its best year ever. That performance in a down year is what cemented its reputation as one of the most sophisticated investment operations in the world.
The Aschenbrenner trade fits naturally into this model. Citadel identified a distressed seller with a large, liquid portfolio and acquired it at a discount. Whether the AI stocks in that portfolio recover determines whether the trade was profitable. Given the prices at which they acquired them, the margin for error was significant.
Citadel Securities: The Other Business
Citadel Securities is a separate entity, though also founded and majority-owned by Griffin. It is not a hedge fund. It is a market maker, and understanding what that means requires a brief detour.
When you buy a stock through a retail broker like Robinhood or most other consumer trading apps, you are not buying directly from another investor who happened to want to sell at that exact moment. You are buying from a market maker, a firm that stands ready to buy and sell securities at all times, profiting from the difference between the price at which they buy and the price at which they sell. This difference is called the spread.
Citadel Securities is one of the largest market makers in the world. At various points it has handled roughly 25% of all US equity trading volume, processing millions of retail trades every day. In 2025 it generated $12.2 billion in trading revenue, a record.
The mechanism by which it receives those trades is called payment for order flow. Retail brokers like Robinhood, rather than sending customer orders directly to a stock exchange, route them to market makers like Citadel Securities. In exchange, Citadel Securities pays the broker a small fee per trade. The broker uses this revenue to offer commission-free trading to customers.
The arrangement attracted significant scrutiny during the GameStop saga of January 2021. Citadel Securities was Robinhood’s largest payment for order flow partner. When Robinhood restricted trading in GameStop during the frenzy, critics alleged a conflict of interest, suggesting Citadel Securities had influenced the decision because its hedge fund arm had exposure to GameStop through a relationship with a short seller. Both Robinhood and Citadel denied any coordination, and subsequent investigations did not produce evidence of wrongdoing. But the controversy brought payment for order flow into public debate for the first time.
Why Citadel Keeps Appearing
The reason Citadel shows up in so many major financial stories is structural. It operates at the intersection of almost everything significant in markets: it runs one of the most active multi-strategy hedge funds, it processes a substantial share of US retail trading volume, and it has the capital and the appetite to act as a buyer of last resort when forced sellers appear.
When markets seize up and someone needs to sell a large position quickly, Citadel Securities is often the entity with both the capital and the information to step in. The Aschenbrenner trade is the most recent example, but it is not unusual in kind.
Whether that concentration of power is healthy for markets is a legitimate question that regulators in both the US and Europe have been asking with increasing urgency. A single firm processing a quarter of retail equity volume and simultaneously running one of the world’s largest hedge funds creates potential conflicts of interest that the industry’s self-regulatory framework has not fully resolved.
For now, Citadel operates within the rules. It does so more profitably than almost anyone else in the world.
Key Takeaways
- Citadel was founded by Ken Griffin in 1990 and has generated $83 billion in net gains since inception, making it the most profitable hedge fund in history.
- Citadel LLC is the hedge fund, running a multi-strategy approach across hundreds of independent portfolio managers. It manages around $69 billion in assets.
- Citadel Securities is a separate market-making business that processes approximately 25% of US retail equity trading volume and generated $12.2 billion in revenue in 2025.
- Payment for order flow is the mechanism by which Citadel Securities pays retail brokers for directing customer trades to them. It became controversial during the GameStop saga in 2021.
- Citadel’s ability to buy Aschenbrenner’s entire portfolio in a single trade reflects its unique position as a firm with the capital and information to act as a buyer when forced sellers appear.