Narration: AI voice.
The number
minus 42.08 billion dollars. That's net GEX on the SPX gamma page for October 15, 2026, computed before the open. Big number. Here's what it measures, and what it doesn't.
Per one percent
Unit first. It's dollar gamma: US dollars of dealer gamma per one percent move in spot. Per one percent, not per point. In plain English, the modeled value of the index the hedging side would trade for a one percent move. The formula, off the page: gamma, times open interest, times the hundred multiplier, times spot squared, times one percent. Calls positive, puts negative. Summed over every contract. That's the sign. Under the page's convention, dealers are long the calls and short the puts. Minus means the put side was larger at the prior close.
The inputs
The inputs. Open interest settled October 14, 2026, across 20,205 contracts. And one assumption nobody can observe: which side the dealer holds. Open interest shows a contract exists. Never who's on which side.
What it is not
Now the trap. Same tile, the label reads positive gamma. The total is computed once, before the open, at the prior session's closing price, 7,718.94, which sat below the flip, and it stands for the session. The label follows where spot is now: 7,744.17, flip 7,729. So on one tile the two can carry different signs.
Wrap
So: dollars of gamma per one percent move, modeled from settled positions, stamped with its time. More on gamma exposure is on the learn page linked below. Educational only.
Full write-up with sources: /learn/what-is-gamma-exposure-gex
Educational content, not investment advice.
Levels shown are as captured on 2026-10-16 01:39 ET; they are not current.