If you only watch one level on the dealer-positioning map, make it the gamma flip. Above it, dealers are net long gamma and their hedging dampens moves. Below it, dealers are net short gamma and their hedging amplifies moves. That single sign change rewires the intraday tape.
What "gamma flip" actually means
Aggregate dealer gamma exposure (GEX) is the sum, across every listed strike on a single underlying, of gamma × open interest × contract multiplier × spot² × 0.01. The result is dollars of delta hedging required per 1% move in spot. When you cumulate that quantity from the put wing to the call wing of the chain, the level where the running total crosses zero is the gamma flip.
Below the flip, the put-wing OI dominates and dealers — who are typically short those puts — need to sell into weakness and buy into strength to stay delta-neutral. That is exactly the hedging behavior that turns small selloffs into cascades. Above the flip, the call-wing OI dominates and the hedging flips to the opposite leg: dealers sell rallies, buy dips. Their books mechanically dampen realized vol.
Why the flip is sticky
Two reasons. First, OI is slow-moving — it changes meaningfully only at expiration. So the flip level rarely moves more than 1–2% intraday. Second, dealers don't choose to flip; the chain's structure does. Even if they wanted to take the other side, they'd be paying the spread to do it. So once the flip is set for the day, it acts as a regime hinge.
Trading the long-gamma side
- Fade extremes. When dealers are long gamma, sharp intraday moves get faded mechanically. Selling near the upper end of the day's range and covering near the flip is the canonical long-gamma trade.
- Sell premium. Long-gamma regimes compress realized vol below implied. Short straddles and iron condors centered between the put wall and call wall harvest the spread.
- Trust the walls. Call walls and put walls hold more reliably in long gamma than short. The mechanical buyer of last resort lives at the put wall.
Trading the short-gamma side
- Trend with the flow. Short-gamma turns dealers into momentum followers. Once a direction sets in, fading it is a low-edge trade.
- Widen stops. Realized vol overshoots implied. Stops that worked in long gamma get hit by noise in short gamma.
- Watch for the reclaim. Crossing back above the flip is the highest-edge regime change — long-gamma machinery snaps on instantly.
Common misreads
Net GEX sign is not the same as the flip level. You can have positive net GEX (long-gamma regime) but still be trading below the flip if the largest call wall is far OTM. The level itself is what matters for intraday — not the total.
Also, single-strike GEX values are noisy. A small chain or a low-OI strike will produce a "flip" near every other strike. Aggregate across the front three expirations and the noise drops out. GEXRadar's gamma flip is computed against the cumulative cross-expiry curve for exactly this reason.
The level to watch tomorrow
For SPY/SPX the flip typically sits 0.3%–1.2% from spot at the open. By 10:30 ET it's usually re-confirmed by the morning auction. If you're trading SPX 0DTE, mark the flip, mark the put wall, mark the call wall — and let your bias come from where spot sits in that range, not from price-action alone.