rozen

The hidden machinery of money & AI. One mechanism nobody explains — broken down every day.

[rozen @rozenhz]

A stock ticks up two cents. Someone bought it. A millisecond later, someone sold it. Both trades were the same machine.

In between them: your order.

This is how a single company in Chicago earns $10 billion a year. Without ever betting on a stock going up or down.
Michael Lewis put it on 60 Minutes in 2014. The book became a bestseller. Congress held hearings. A new exchange opened just to fight it.
Nothing broke the machine.
Here's exactly what it does.
You place an order. A machine somewhere else sees it before the exchange does. Buys the stock a millisecond earlier. One cent cheaper. Two cents cheaper. Then turns and sells it back to you.
You never see the trade.
You never see the machine.
You just get filled a fraction late, at a fraction worse.
One cent. Two cents.
Billions of shares a day.
That's not gambling. That's a toll booth.
The company is called Citadel Securities. It handles more than a third of every retail trade in America. The man who built it is Ken Griffin. Forty-three billion dollars, and not one of them came from being right about a stock.
He doesn't predict where prices go. He gets paid every time prices move at all.
The stock market isn't a place where prices are discovered.
It's a place where prices are sold to you.
Fourteen minutes below. It will change every trade you place after.

[rozen @rozenhz]

I break down one of these every day. Follow so the next one doesn't get past you.

[rozen @rozenhz]

The firm that takes a cut of every trade you make just did the one thing it never lets you get away with.

It guessed.

And it cost them $15 billion in a single month.

Jane Street is the machine that sits between you and the market. Every time you buy, every time you sell, it skims a fraction of a cent. It never bets. It never picks a side. It just collects.

For ten years straight, it never had a single losing month.

Because it never plays the game it sells to you.

Then in July, it broke its own rule. It took a side. It bet on AI going up, through a fund built on the "situational awareness" thesis about where the whole AI race was headed.

AI stocks dropped. The bet dropped with them.

$15 billion, gone. First red month in a decade.

Here's what it means for you: the people who profit off your every move are only untouchable while they refuse to move themselves.

The house doesn't lose at the table. It loses the second it sits down like the rest of us.

Clip below shows the empire that runs it. Last month, for the first time, it cracked.

[rozen @rozenhz]

I break down one of these every day. Follow so the next one doesn't get past you.

[rozen @rozenhz]

For 120 months in a row, one trading firm never lost money. Not a single red month.

Then in July, it lost $15 billion.

Jane Street doesn't guess where the market goes. It sits between every trade and keeps a fraction of a cent. No direction. No risk. No losses. For ten straight years.

Then it did the one thing it never does.

It took a side.

It bet on AI going up, through a fund built on the "situational awareness" thesis about where the whole AI race was heading.

AI stocks cracked in July. The bet cracked with them.

$15 billion. First red month in a decade.

The machine only wins as long as it refuses to play the game it sells to everyone else.

The house doesn't lose at the table. It loses the second it sits down at one.

Clip below shows the empire that built it. Worth every second.

[rozen @rozenhz]

internalization, yeah. i was loose calling it a technicality and you're right to catch it. the law drew that line on purpose, agreed. only thing i'd add: a line can be intentional and still be worth a fortune to whoever sits on the right side of it. the rules are clean. who benefits from them isn't evenly spread. that's the part i watch.

[rozen @rozenhz]

THE MOST ASKED QUESTION UNDER THIS POST WAS "HOW IS THIS LEGAL."

the answer is worse than the trade itself.

front-running someone's order is a federal crime. people go to prison for it.

what citadel does is the same idea, rebuilt so precisely that no law can touch it.

[rozen @rozenhz]

A stock ticks up two cents. Someone bought it. A millisecond later, someone sold it. Both trades were the same machine.

In between them: your order.

This is how a single company in Chicago earns $10 billion a year. Without ever betting on a stock going up or down.
Michael Lewis put it on 60 Minutes in 2014. The book became a bestseller. Congress held hearings. A new exchange opened just to fight it.
Nothing broke the machine.
Here's exactly what it does.
You place an order. A machine somewhere else sees it before the exchange does. Buys the stock a millisecond earlier. One cent cheaper. Two cents cheaper. Then turns and sells it back to you.
You never see the trade.
You never see the machine.
You just get filled a fraction late, at a fraction worse.
One cent. Two cents.
Billions of shares a day.
That's not gambling. That's a toll booth.
The company is called Citadel Securities. It handles more than a third of every retail trade in America. The man who built it is Ken Griffin. Forty-three billion dollars, and not one of them came from being right about a stock.
He doesn't predict where prices go. He gets paid every time prices move at all.
The stock market isn't a place where prices are discovered.
It's a place where prices are sold to you.
Fourteen minutes below. It will change every trade you place after.

[rozen @rozenhz]

honestly we agree. liquidity is essential, two-sided quotes keep the market alive, i know the plumbing. i'm not anti-market-maker. the only thing i flagged is one firm having visibility into most of the country's retail orders. that's a scale point, not a "kill the MMs" point. think we're just talking past each other at this point.

[rozen @rozenhz]

A stock ticks up two cents. Someone bought it. A millisecond later, someone sold it. Both trades were the same machine.

In between them: your order.

This is how a single company in Chicago earns $10 billion a year. Without ever betting on a stock going up or down.
Michael Lewis put it on 60 Minutes in 2014. The book became a bestseller. Congress held hearings. A new exchange opened just to fight it.
Nothing broke the machine.
Here's exactly what it does.
You place an order. A machine somewhere else sees it before the exchange does. Buys the stock a millisecond earlier. One cent cheaper. Two cents cheaper. Then turns and sells it back to you.
You never see the trade.
You never see the machine.
You just get filled a fraction late, at a fraction worse.
One cent. Two cents.
Billions of shares a day.
That's not gambling. That's a toll booth.
The company is called Citadel Securities. It handles more than a third of every retail trade in America. The man who built it is Ken Griffin. Forty-three billion dollars, and not one of them came from being right about a stock.
He doesn't predict where prices go. He gets paid every time prices move at all.
The stock market isn't a place where prices are discovered.
It's a place where prices are sold to you.
Fourteen minutes below. It will change every trade you place after.

[rozen @rozenhz]

fair distinction, and you're right that it's not literally front-running. but your analogy is missing a piece. this wholesale distributor doesn't just keep the booth open. they pay to see every buyer's order before it reaches the booth, then decide how to fill it. a normal distributor doesn't get that. the legality isn't the interesting part. the information asymmetry is.

[rozen @rozenhz]

yeah it's wild how far it goes. they pay exchanges to place their servers a few feet closer to the matching engine. and there's a famous cable dug in a straight line from chicago to NY through mountains just to shave milliseconds. now they use microwave and laser links because light through air beats fiber. the doc was probably flash boys

[rozen @rozenhz]

@heynow987 @realDonaldTrump @TrumpsPortfolio @JDVance @defense_civil25 @FT @elonmusk @DOGE appreciate the share. one nuance though — it's technically not front-running (that part's actually illegal). what makes this one hard to fix is that it's legal by design, they fill you at the official best price. that's exactly why it's so hard to just "ban."

[rozen @rozenhz]

that's the whole game.

the illegal version gets you a cell. the legal version gets you a $238m penthouse.

same move. different paperwork.

i break down one of these every day. follow so the next one doesn't get past you.

[rozen @rozenhz]

and this isn't a theory someone's guessing at.

the SEC fined robinhood $65 million in 2020 over how they disclosed this to customers.

a fine. not criminal charges. because no crime was committed.

that's the tell. the penalty for the biggest version of it is basically a receipt.

[rozen @rozenhz]

@samura1ij "survive being wrong long enough to be right" is the realest line here. everyone's optimizing which stock to pick when the actual game is whether you can watch the number drop for 18 months and do nothing. patience is the alpha nobody markets

[rozen @rozenhz]

you're right that market makers are necessary, pull them out and liquidity dries up, orders sit, no argument there. the post isn't "MMs are a bug". it's that one firm seeing a third of all retail flow and getting paid for it is a scale thing, not a "should MMs exist" thing. the liquidity tax being real doesn't mean the concentration isn't worth noticing

[rozen @rozenhz]

@Sxfinafrohlich yeah crypto might be the purest example of it. there's a whole hidden layer called MEV where bots front-run your trade the second you hit send. honestly that's a rabbit hole worth its own breakdown. same machine, different playground

[rozen @rozenhz]

@hamburgler66 yeah honestly that's a fair take, zero commission genuinely helped regular people. the only thing i'd add is "free" isn't quite free, the old commission just turned into a spread you don't see. still way cheaper than the old days though, you're right about that

[rozen @rozenhz]

honestly i'd bet the opposite. citadel IS one of the most advanced AI shops on the street already. if retail starts trading through AI agents, that's just more order flow for them to price and route. the guy with the fastest machines doesn't lose when everyone switches to machines, he wins bigger

[rozen @rozenhz]

@DanielSickah lewis writes nonfiction actually (big short, moneyball). and PFOF is documented fact, the SEC fined robinhood over it. which specific part are you saying isn't factual? genuinely asking

[rozen @rozenhz]

@The2ndDrOrgel yeah fair, HQ is miami now. the clip's a little dated. doesn't really change the mechanics though, the flow routes the same no matter what city the servers bill from