The Volatility Trigger: The Level That Sets the Vol Regime

Summary. The gamma flip marks where dealer hedging changes direction. The volatility trigger marks where that hedging becomes large enough to change the character of the market. This article derives a simple price-impact model in which dealer gamma scales realized volatility, uses it to show why the two levels differ, and discusses how practitioners define the trigger and trade around it.

1. Two questions, two levels

The gamma flip answers a sign question: at which spot level does aggregate dealer gamma exposure (GEX) cross zero? Above it, hedging leans against moves; below it, hedging follows them. The volatility trigger answers a magnitude question: at which level does hedging flow become large relative to the liquidity available to absorb it?

The term is practitioner vocabulary rather than an academic standard, and definitions differ between vendors. SpotGamma, which popularized it, describes its trigger as the last major level of positive gamma support, and notes that it can sit several points above the zero-gamma level [1]. In DataFirst, the trigger is placed where modeled dealer selling starts to accelerate, which is usually close to the flip and often just below it, near the heaviest concentration of short put gamma. Both definitions try to locate the same thing: the point where hedging stops being a background force and starts to drive the tape.

2. A minimal model of hedging and volatility

Let $F$ be exogenous net order flow in dollars and $L$ the dollar flow needed to move the index by 1%. Without dealers, the return in percent is $r=F/L$. Dealers with gamma exposure $G$ (dollars of delta per 1% move) add a hedge trade of $-Gr$. The return then solves

The multiplier $m(S)$ scales realized volatility. When $G>0$, $m<1$ and moves are damped. When $G$ is negative, $m>1$ and moves are amplified. As $G$ approaches $-L$, the multiplier grows without bound, which is the model's version of an air pocket. This is a static, linear simplification of feedback models of hedging such as those studied by Barbon and Buraschi and by Anderegg, Ulmann and Sornette [2, 3], and it is useful for intuition rather than for forecasting.

Figure 1 applies the model to the same hypothetical chain used in the other articles. Above the flip (about 5,967) the multiplier is below one. Just below the flip it rises slowly, because net gamma is negative but small. Further down, the put-heavy strikes dominate and the multiplier climbs quickly. Defining the trigger as the level where $m$ exceeds 1.25, it sits near 5,915 in this example. The exact threshold is a choice; the point is that there is a band between the flip and the trigger where dealers are short gamma but the amplification is still mild.

3. The band between the levels

Figure 2 shows the same two levels on the GEX profile itself. The trigger is where net GEX falls to minus 20% of the assumed liquidity, the point at which $m=1.25$.

Between the flip and the trigger, the tape often looks noisy rather than trending. Hedging works with the move, but the flow is small relative to liquidity, so pullbacks are shallow and dip buying can still work. This band misleads traders because it feels like an ordinary pullback.

Below the trigger, the hedge flow per point grows faster than liquidity. Each additional point lower requires more selling, realized volatility rises above implied, and mean-reversion trades lose their edge. Evidence that short-gamma hedging produces intraday momentum, especially late in the session, is documented by Baltussen, Da, Lammers and Martens across more than 60 futures markets [4].

4. How to trade around it

A reclaim of the trigger from below is usually the first sign of stabilization and tends to come before a reclaim of the flip. It shows that hedge flow is shrinking relative to liquidity, even though dealers may still be net short gamma.

5. Why it matters more for 0DTE and futures

Same-day options concentrate gamma in a narrow band around spot, so the GEX curve can change shape within hours and the trigger can move with it. The 0DTE mechanics article quantifies how narrow that band becomes late in the session. For E-mini futures traders the trigger translates directly into futures prices after adjusting for the basis, as described in using options flow to trade ES and NQ.

6. Limits

• The model treats liquidity $L$ as constant. In practice liquidity falls when volatility rises, which makes amplification worse than the model suggests.
• Dealer positions are estimated with a sign convention, and errors in that convention move both levels.
• Gamma depends on implied volatility. A volatility spike widens gamma profiles and changes both curves.
• Vendors use different definitions. Compare levels only within one methodology.

For educational and informational purposes only. Not financial advice. Options and futures trading involve substantial risk of loss. Figures use a hypothetical option chain and a stylized impact model.

References

1. SpotGamma. Volatility trigger and zero gamma. Practitioner note. spotgamma.com/volatility-trigger-zero-gamma-trading/
2. Barbon, A., & Buraschi, A. (2021). Gamma fragility. Working paper, University of St. Gallen. SSRN 3725454. papers.ssrn.com/sol3/papers.cfm?abstract_id=3725454
3. Anderegg, B., Ulmann, F., & Sornette, D. (2022). The impact of option hedging on the spot market volatility. Journal of International Money and Finance, 124, 102627. doi.org/10.1016/j.jimonfin.2022.102627
4. Baltussen, G., Da, Z., Lammers, S., & Martens, M. (2021). Hedging demand and market intraday momentum. Journal of Financial Economics, 142(1), 377–403. doi.org/10.1016/j.jfineco.2021.04.029