Why it matters
Market makers sit on the other side of most options trades, and they do not want directional risk. They hedge with stock, and the amount they must hedge changes as price moves. Gamma is the name for that rate of change. Add it up across every open contract on a ticker and you get gamma exposure: a map of where hedging flows are large and which way they push.
The direction is what makes it useful. Where exposure is positive, hedgers buy as price falls and sell as it rises, which leans against the move and tends to hold price in a range. Where exposure is negative, hedgers sell into weakness and buy into strength, which adds fuel to whatever move is already underway. The GEX heatmap shows this as a grid: strikes down the side, expirations across the top, gold cells where positive gamma clusters and purple where it turns negative, with the spot price marked so you can see which zones are in play.
Two summaries fall out of the map. The net figure across all strikes gives the ticker's gamma regime, positive or negative. The strikes with the heaviest concentrations are the call wall and put wall, the levels most likely to slow a move.
What it does not tell you
- It is an estimate, not a position report. Nobody publishes what market makers hold. Gamma exposure is built from open interest and standard assumptions about which side dealers are on. Different sites make different assumptions, so figures differ by source.
- It has no direction of its own. Positive gamma says moves are likely to be dampened, negative says they are likely to be amplified. Neither says which way price goes.
- It expires. A large part of any ticker's exposure sits in the nearest expirations. When those contracts expire, the map can change shape overnight.
- Public data is delayed. Symbol pages show the session three trading days ago. The heatmap in the app is current.
What it looks like in the data
AMZN closed the September 14, 2026 session in a positive gamma regime, with price sitting inside the range between its two walls.
Positive regime: net exposure of +$157.9M means hedging leaned against moves in both directions that session. The walls at $240 and $260 bracket the close by 5.4% below and 2.5% above. Drawn to scale. Not a price target.
On the heatmap for that session the gold cells, the positive magnets, ran across nearly every expiration in one strike row above the close, the call wall at $260, with two more at the spot row itself. The purple negative zones sat in the rows just below the close and again lower down, near the put wall at $240, in the later expirations. Read together: a stock trading inside a positive-gamma band, with the heavier wall on the upside and the soft ground underneath. What it did next is not something the map decides.
