Options & dealer gamma

OPEX week. SPX has enormous call open interest at 6,100. ES hovers 6,085–6,095 all week — every rally to 6,098 gets sold, every dip to 6,085 gets bought. Your breakout system fires twice; both fail at 6,098. Nothing is wrong with your reads. The market may be pinned — held near the strike by hedging flows you can’t see on the footprint. This lesson is the trailer; Module 9 is the full film.

The core idea: market makers (nhà tạo lập thị trường, dealers) take the other side of customers’ option trades — short where customers are long, long where customers are short. To stay neutral they hedge (phòng hộ): when the underlying moves, their hedge needs change, so they buy and sell ES/SPX futures mechanically — not on opinion. These flows are real supply and demand, and on big positioning days they’re the largest flows in the market.

Short gamma → amplification: when dealers are short gamma at the strikes near spot (customers bought those options), a rally forces them to buy futures into strength, a selloff forces them to sell into weakness. Their hedging adds fuel to the move — pro-cyclical, buy-high-sell-low, mandatory.

Long gamma → dampening: when dealers are long gamma, hedging fades moves — sell rips, buy dips. Ranges compress, breakouts fail, and your trend system starves.

Pinning (ghim giá) into expiry: when dealers are net long gamma at a large strike into expiry, their hedging sells rallies and buys dips around it, which can hold price near the strike. If they are short gamma there, the same strike can instead accelerate a break. Pinning is well documented for single stocks; for index futures the evidence is mixed (one practitioner NQ test of monthly-expiry range compression was inconclusive). Note expiries as a range risk, and size down, rather than assuming a pin.

Your calendar (lịch): monthly OPEX (third Friday), quarterly triple-witching (Mar/Jun/Sep/Dec — index futures, index options, and single-stock options expire together = maximum mechanical flow, wildest closes). On those weeks: allow for slower trends into large strikes, and for larger moves after expiry once those hedges are gone — possibilities to plan for, not certainties.

Figure: SPX into OPEX Friday: price line oscillating 6,085–6,095 all week around the 6,100 strike (marked “max OI — the pin”). Two failed breakout arrows at 6,098. Monday after expiry: a gap to 6,120 on the same news flow. Caption: “One possible expiry week: a pin that held. Not every expiry looks like this.”

For now, three working rules (mechanics in M9):

1. Some “random” chop around big strikes is mechanical — respect it, don’t fight it.
2. On expiry weeks, if price is visibly holding near a big strike, favor range logic and smaller size over breakouts through it.
3. A held pin can release the session after expiry — plan for that possibility, not just the pin.

Worked example: OPEX week (from the hook). SPX enormous call OI at 6,100; ES 6,085–6,095 all week. Your M5 breakout triggers long twice — both fail at 6,098. Correct read of orderflow, wrong auction: expiry mechanics overruled intraday flow. Monday after expiry, ES gaps to 6,120 on the same news that couldn’t move it Friday. Lesson: in a week like this one, where the strike visibly held, the pin is a possible regime — recognize it from price behavior and trade accordingly. The breakout system wasn’t broken; it was deployed in the wrong week.

Common mistake: Treating pinning as “manipulation” and fighting it (“the market should break out, so I’ll keep buying”). “Should” is not a position. Hedging flows don’t care about your thesis — the professional response to a market that is visibly holding a strike is smaller size and range logic, not louder opinions. The opposite mistake is assuming every expiry pins.

Recap:

• Dealers take the other side of customer option trades and hedge mechanically; short gamma amplifies moves, long gamma dampens them — real supply/demand with no opinion behind it.
• Into big expiries, price can pin near large strikes when dealers are long gamma there; evidence for index pinning is mixed, so treat it as a range risk, not a certainty.
• Calendar the expiries (monthly OPEX, quarterly triple-witching); on those weeks size down and favor range logic when price is visibly holding a strike.

Quiz: It’s quarterly triple-witching Friday. ES has chopped 6,085–6,095 all week under a 6,100 call pin. Your trend system fires a breakout long at 6,098 with textbook acceptance. Take it at full size? Answer: No — reduce size drastically or skip; trade the range instead. Explanation: a pin is a possible regime, not a law — but this week’s price behavior (a week of chop under 6,100 and two failed breakouts) is evidence that something is holding the strike, and expiry is a known range risk. Full size on a breakout into that is a bad bet even if it might work. The full-size breakout belongs to next week, when expiry hedges are gone.

Further reading:

• Gamma Exposure (GEX) (SqueezeMetrics white paper) — the originating document: the four dealer-positioning assumptions and the gamma-regime mechanism.
• Gamma, Vanna, Charm and How Options Influence the Market (Brent Kochuba) — the video primer: delta hedging, the OpEx cycle, flows driving the index — M9’s trailer in motion.

Connects to: M8.05 (the fear gauge above the mechanics) → M9.01 (Module 9: the full dealer-flows toolkit).

Educational content only — not financial advice. Futures trading involves substantial risk of loss.