Dealer positioning: gamma, vanna and OPEX
One of the biggest market movers, and one almost no retail course explains: how options market makers (dealers) hedge. They don't bet on direction; they buy and sell the underlying to stay neutral, and that mechanical — sometimes enormous — hedging pushes the price. Here are gamma, vanna, charm and why the market "pins" or explodes at expirations.
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Who's on the other side: the dealer
When you buy or sell an option, on the other side there's usually a market maker. It doesn't want to bet on direction: to stay neutral it buys or sells shares of the underlying (it adjusts its "delta"). If the market moves, it has to rebalance that hedge again and again. That mechanical buy/sell flow, multiplied by millions of contracts, leaves a real footprint on the underlying's price.
Gamma exposure (GEX)
Gamma measures how much the delta (the hedge) changes when the price moves. GEX sums the gamma dealers hold at each strike. With POSITIVE gamma (dealers long gamma) they buy dips and sell rallies → they dampen volatility and the market turns "sticky". With NEGATIVE gamma (dealers short) they do the opposite: they sell dips and buy rallies → they amplify the move and spike volatility.
Pinning and max pain
Near an expiration with high gamma, dealer hedging tends to "pin" the price to the strikes with the most open interest. It's the magnet effect: each time price drifts away, the hedge pulls it back. The level where the most options would expire worthless is called "max pain" and often acts as a magnet. That's why on expiration day the price sticks to a round number more often than looks like chance.
Gamma squeeze
When dealers are heavily short gamma — for example because the crowd has bought mountains of calls — every rise forces them to buy more of the underlying to hedge. That buying pushes the price even higher, which forces them to buy still more… a self-reinforcing loop that shoots the price up violently. It's what amplified the GameStop case in 2021. It works the same way to the downside with puts.
Vanna: IV pushes the delta
Vanna measures how the delta (the hedge) changes when implied volatility (IV) changes, not the price. With high, positive vanna, a simple DROP in IV forces dealers to BUY the underlying to rebalance → upward pressure without anything "happening" in the news. It's the explanation for those slow rallies "just because the VIX is falling". It dominates in environments where volatility, not price, is what's moving.
Charm: the OPEX drift
Charm measures how the delta changes with the mere passage of time. As expiration approaches, the delta of in-the-money options accelerates toward 1 (calls) or −1 (puts), so dealers have to buy or sell the underlying even if the price doesn't move. That clock-driven rebalancing produces the "drift" — often bullish — so typical of expiration week. It's time, not direction, that moves the flow.
0DTE and OPEX: pin or break
Options that expire the same day (0DTE) and the big expirations (the third Friday, the quarterlies) concentrate enormous gamma into a few hours. The result has two faces: while the level holds, hedging pins the price and volatility dies down; but if a push breaks that level, the hedge flips at once and the move turns violent. These are the days when dealer flow rules more than the news.