Open interest & GEX/DEX maps

Thursday morning. SPX 6,000. Your GEX map shows +$2B gamma above 5,985 and −$1.5B below it. All morning ES chops 5,995–6,010 — every push gets sold. 13:30: a headline breaks 5,985 on volume, and ES flushes to 5,958 in 40 minutes. The map didn’t predict the headline. It told you what the market would do with it: contained above the line, violent below. That line has a name.

OI by strike (vị thế mở theo giá thực hiện): outstanding contracts per strike — where real positioning sits. Unlike volume (one day’s activity), OI is commitment. Big-OI strikes are battlegrounds: into expiry, price can pin near them when dealers are long gamma there — index evidence is mixed (pinning, M9.06); away from expiry, they’re decision zones — expect absorption and two-sided trade there. Changes beat levels: a strike whose call OI doubled this week matters more than one that’s always big. Put/call OI ratio reads sentiment like COT (M8.05): crowdedness, never timing.

GEX (độ phơi nhiễm gamma) = the market’s estimate of dealers’ net gamma by strike, in dollars per point. Positive GEX (dealers long gamma) → hedging fades moves → compression, failed breakouts. Negative GEX (dealers short gamma) → hedging fuels moves → trends accelerate, air pockets below/above.

The flip point (điểm đảo gamma): where net gamma crosses zero — the single most-watched level on the map. Above it: dampen. Below it: amplify. It migrates as spot moves and expiries pass — check it every morning, not weekly.

DEX (delta exposure): the net delta of open options by strike. Check the vendor’s sign convention before reading it: some publish DEX holder-signed (the customer side), others dealer-signed, and the same number means opposite things under the two. Delta describes the hedge that already exists; the new hedging flow as price moves comes from gamma (GEX). Sibling to GEX, not a replacement.

Data honesty: GEX is estimated (ước tính) — models infer dealer positioning from OI and trade data, and providers disagree on the dollars. Use the zones, the flip, and the sign — never the exact figures, never a GEX number alone as a trigger.

Figure: GEX map schematic: SPX 6,000 center. Bars above 5,985 tall and green (+$2B, “dealers long gamma → chop zone”). Bars below 5,985 red (−$1.5B, “air pocket → 5,950 put wall”). Vertical line at 5,985: “FLIP — the regime boundary.” Caption: “Above: compression. Below: acceleration.”

Worked example: the hook, traded. Morning map: flip 5,985, +$2B above, −$1.5B below to the 5,950 put wall. Morning sheet wrote both scenarios before the open: “above flip → fade extremes, half size on breakouts; below flip on volume → the flush has fuel, trade with it.” 13:30 headline breaks 5,985 with real volume — the M5 short triggers with delta confirmation; target the 5,958 air pocket (from the map), filled by 14:10. By 15:30 the flush exhausts and ES bounces as hedges unwind. The map wrote the script; orderflow confirmed each act. Without the map, the same short is “trading the news” — with it, it’s trading a regime transition the map located in advance.

Common mistake: Treating the flip point as a trade signal — “price crossed the flip, short!” The flip is a regime boundary, not an entry trigger. Crossings without volume and orderflow confirmation are noise; the map provides context (where moves accelerate), and entries still come from M3/M5 tools. GEX as signal is numerology; GEX as context is edge.

Recap:

• OI-by-strike shows positioning commitment; changes matter more than levels; put/call OI ratio reads crowdedness, never timing.
• GEX maps dealer gamma: positive = compression, negative = acceleration; the flip point divides the regimes and migrates daily.
• GEX is estimated — trade the zones/sign/flip, never exact dollar figures, and never as a standalone trigger.

Quiz: Two providers show +$1.2B and +$2.8B gamma above spot — wildly different dollars — but both place the flip at 5,985 and agree gamma is positive above, negative below. A trader says the disagreement “invalidates the tool.” Are they right? Answer: No. Explanation: the dollars are model estimates and always disagree; the robust outputs are the sign, the zones, and the flip location — which agree. Regime identification (compression above 5,985, acceleration below) survives estimation error; precise figures don’t. The trader is demanding false precision from a context tool — the map was never a measuring instrument, it’s a weather map.

Further reading:

• Gamma Exposure (GEX) (SqueezeMetrics white paper) — the originating document: the four assumptions and the positive/negative gamma mechanism.
• Dark Index (DIX) & GEX Monitor (SqueezeMetrics) — the live data + methodology: how DIX and GEX are actually built and read.
• Gamma Exposure (GEX): How Dealer Hedging Moves SPX (FatTail) — the flip as regime boundary, strike magnets, 0DTE implications — framed as a filter, not a signal.

Connects to: M9.03 (the vol the positioning is priced in) → M9.05 (walls — the same positioning, strike by strike).

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