Gamma Exposure (GEX)
Canonical definition, formula, interpretation rules, and live API reference for dealer gamma exposure.
The net dealer gamma exposure derived from option open interest weighted by per-strike gamma. Measures how much dealers must buy or sell as the underlying moves, driving intraday support and resistance levels.
Where Γᵢ is the Black-Scholes gamma of contract i, OIᵢ is open interest, S is spot price, sign is +1 for calls and -1 for puts, and the sum is across the entire option chain.
- Positive GEX: dealers long gamma. Buy dips, sell rips. Mean-reverting regime, dampened volatility.
- Negative GEX: dealers short gamma. Sell dips, buy rips. Trending regime, amplified volatility.
- Gamma flip: price level where the sign transitions. Acts as the key intraday pivot.
Live Example: SPY
Live SPY GEX data temporarily unavailable. See /stock/spy/gamma for current values.
Get GEX via API
symbol(path, required) — underlying ticker, e.g.SPYexpiration(query, optional) — filter to single expiry (yyyy-MM-dd)min_oi(query, optional) — minimum open interest threshold
{
"symbol": "SPY",
"underlying_price": number,
"gamma_flip": number,
"net_gex": number,
"net_gex_label": "positive" | "negative",
"strikes": [
{ "strike", "call_gex", "put_gex", "net_gex",
"call_oi", "put_oi", "call_volume", "put_volume" }
]
}curl -H "X-Api-Key: YOUR_KEY" \
https://lab.flashalpha.com/v1/exposure/gex/SPYWhy GEX Matters for Trading
GEX tells you whether dealer hedging will dampen or amplify price moves. Positive GEX → mean-reversion regime, range strategies work. Negative GEX → trending regime, momentum and long-vol work. The gamma flip is the pivot between the two.
- What it measures
- Dealer hedging intensity. Higher absolute GEX means dealers must trade more shares per 1% move to stay delta-neutral.
- What it signals
- The regime — whether dealer flow will mute volatility (positive) or amplify it (negative), not the direction of the next move.
- Why we measure it
- Dealer gamma hedging is one of the largest non-discretionary flows in US equity markets. Knowing the sign and size of GEX lets you pick strategies that align with (rather than fight) that flow.
- Who uses it
- Market makers, vol traders, 0DTE specialists, dealer-flow quants, and discretionary traders looking for a regime filter.
How to read different GEX regimes
- Price chops and reverts to center
- Realised vol compresses below implied
- Call/put walls act as strong S/R
- Dealers buy dips, sell rallies
- Small moves cascade into big moves
- Realised vol expands above implied
- Walls get broken, not defended
- Dealers sell dips, buy rallies
- Regime is unstable; small catalysts flip it
- Expect whippy, two-way price action
- Wait for a clean break of the flip before sizing up
- Intraday breakouts become more reliable once flip holds
Rules of thumb
- Sign beats magnitude. GEX scales with notional size, so $2B positive on SPY and $50M positive on TSLA carry the same signal — both are "long gamma". Compare a ticker to its own recent range, not across names.
- Regimes lock in away from the flip. Treat GEX signals seriously only when spot is comfortably above or below the gamma flip. Hugging the flip means any small move can reverse the regime.
- GEX is not directional. It tells you how price will move, not where. Pair with DEX (net delta) for direction, VEX for vol sensitivity.
- 0DTE GEX dominates intraday. The 0DTE magnet strike can override the full-chain picture in the final hours of expiration day.
- Ignore GEX around catalysts. CPI, FOMC, earnings — gamma hedging gets overwhelmed by directional event flow. Don't trade GEX signals into known risk windows.
How to Read GEX
Start with the sign. Positive net GEX means dealers are net long gamma across the chain. When price moves against them, they re-hedge by trading with the move — buying dips and selling rallies — which dampens volatility and creates mean-reverting intraday conditions. This is the regime where range-bound strategies, credit spreads, and iron condors tend to work. Negative net GEX flips the behaviour: dealers sell into declines and buy into rallies, amplifying moves in both directions. This is the regime where trend-following and breakout strategies tend to work, and where mean-reversion gets hurt.
Then look at the gamma flip — the price level where net GEX crosses zero. This is the single most important intraday pivot because it marks the boundary between the two regimes. If spot is above the flip, the positive-gamma mean-reversion regime dominates. If spot breaks below, dealer hedging flips to amplification. Many discretionary traders use the gamma flip as their primary trend filter.
Per-strike GEX (available from the API) adds a layer of context: the strikes with the highest absolute gamma are the call wall and put wall. In positive gamma, price tends to oscillate between them. In negative gamma, a break through either wall usually accelerates.
Related Concepts
The price level where net GEX crosses zero — the boundary between positive and negative gamma regimes.
The strike with the highest call gamma concentration — acts as intraday resistance in positive-gamma regimes.
The strike with the highest put gamma concentration — acts as intraday support in positive-gamma regimes.
The directional sibling of GEX — net delta dealers must hedge across the chain.
How delta changes with implied volatility — the vol-coupling layer above GEX.
The strike where total option holder loss is minimized at expiration — often aligns with gamma flip near expiry.
Learn More
Complete guide with dealer mechanics, historical examples, and trading applications.
Full endpoint reference with parameters, response schema, and tier limits.
Per-strike gamma exposure visualisation for any US equity or ETF.
Practical strategies for trading the positive and negative gamma regimes.
Frequently asked questions
- What is GEX in options trading?
- GEX (Gamma Exposure) is the net dealer gamma exposure, computed as the sum across all options of gamma × open interest × 100 × spot, with call gamma counted positive and put gamma counted negative. It measures how many shares dealers must buy or sell for each 1% move in the underlying to stay delta-hedged. Positive GEX means dealers buy dips and sell rips (mean-reverting regime). Negative GEX means dealers sell dips and buy rips (trending, amplified regime).
- How is gamma exposure calculated?
- For each option contract, gamma exposure = gamma × open interest × 100 × spot price. Sum across all calls (positive) and puts (negative) for net GEX. Per-strike GEX aggregates contracts by strike price. The calculation assumes dealers are short the public's net options position, which is the standard industry assumption.
- What is the difference between positive and negative GEX?
- Positive GEX means dealers are long gamma. As price falls, they buy the underlying to re-hedge; as price rises, they sell. This creates mean-reversion and dampens volatility. Negative GEX means dealers are short gamma. As price falls, they sell to re-hedge; as price rises, they buy. This amplifies moves and creates trending, volatile conditions. The gamma flip is the price level where these two regimes switch.
- How do I get real-time gamma exposure data via API?
- FlashAlpha's GET /v1/exposure/gex/{symbol} endpoint returns per-strike gamma exposure, net GEX, gamma flip, and the positive/negative regime label for any US equity or ETF. Free tier covers single-expiry GEX; Growth tier covers full-chain GEX aggregated across all expirations. Example: curl -H 'X-Api-Key: YOUR_KEY' https://lab.flashalpha.com/v1/exposure/gex/SPY
- Why does GEX matter for trading?
- GEX tells you whether dealer hedging flow will dampen or amplify price moves. In positive GEX, dealers buy dips and sell rallies, suppressing volatility and creating mean-reverting conditions that favour premium sellers, iron condors, and range strategies. In negative GEX, dealers sell dips and buy rallies, amplifying moves and favouring long straddles, momentum strategies, and breakout trades. Aligning strategy to regime is one of the highest-leverage uses of options flow data.
- When is GEX good versus bad for a trader?
- Positive GEX is good for premium sellers (short strangles, iron condors, 0DTE credit spreads) and bad for breakout traders. Negative GEX is good for premium buyers (long straddles, directional calls/puts) and trend followers, and bad for short-vol strategies. Readings near the gamma flip are a transition zone - wait for a clean break before committing size. GEX is unreliable across major catalysts (CPI, FOMC, earnings) when directional event flow overwhelms dealer hedging.
- What is a good threshold for 'high' GEX?
- There is no universal threshold because GEX scales with the underlying's notional size. SPY typically ranges from -$5B to +$10B; a single stock like TSLA might range from -$200M to +$500M. The meaningful signal is not the absolute level but the sign (positive vs negative) and change day-over-day. Sustained positive GEX above the average means dampening; sustained negative GEX below the average means amplification.
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