5. Era One: Levels from Open Interest

5. Era One: Levels from Open Interest

Every morning, before trading opens, the exchanges publish a digest of the previous day: how many option contracts stand open at each strike. One table of numbers. Around the habit of reading it correctly an entire industry has grown up — options analytics services, morning newsletters with "levels for today," terms every other trader now knows by heart: walls, magnets, the gamma flip. Let's work out how a table of positions turns into lines on a chart — and why it works.

The raw material: the daily snapshot

The analyst of this era has two ingredients at his disposal. The first is open interest at each strike: those same accumulated positions from lesson 2, published by the exchange once a day, as of yesterday's close. The second is live option quotes, from which, as we know, IV is extracted and the greeks are computed.

Mix the two and you get a map: which strikes hold the big money, and what greeks those positions carry. Everything that follows is interpretation of that map.

The OI profile: where the money sits

The most direct way to look at the table is to unfold it along the price axis.

Each row is a strike. Green bars to the right are open interest in calls, red bars to the left are puts. The dashed line is the current price. Even with no theory at all, the map reads itself: puts crowd below the market (insurance against a fall — remember the portfolio manager from lesson 1), calls sit above it (bets on a rally). And most tellingly, the positions are not spread evenly: the money clusters into nodes at round strikes.

Why is an OI node a level on the price chart? Two reasons pull in the same direction. First, a lot of money is tied to a large strike, and as price approaches, its owners and sellers start acting — trading thickens around the node. Second — and this is the main mechanism — gamma is concentrated at a large strike, which means the dealers' forced scrambling from lesson 4 peaks right beside it: in long gamma mode their hedging trades against every deviation, and price bogs down near the strike as if in honey.

The walls and the magnet

Three levels from this map became classics; you will meet their names in any options service — and in our indicator suite.

Call wall — the strike with the largest call OI, 6100 in the picture. A classic resistance: approaching it from below, the market often slows — hedging thickens, call sellers defend the level.

Put wall — the mirror-image strike in puts, here 5800. A classic support.

Max pain — the strike at which a close would inflict the greatest combined losses on option buyers (and, accordingly, the greatest gains on sellers). Here it sits around 6000. The observation that gave the level its name: by expiration, price winds up suspiciously often somewhere nearby. There is no mysticism in it — it is the same pin from lesson 4: the hedging of large sold positions itself pulls price toward the strikes where those positions are thickest.

All three levels share one property worth saying out loud: they work harder the closer expiration gets — because their strength grows out of gamma, and gamma, as we saw in lesson 3, sharpens toward the end of an option's life.

The GEX profile: from positions to forces

The OI profile answers the question "where does the money sit." The era's next step was the question "what forces does that money create." To answer it, every position in the table is multiplied by its gamma and summed strike by strike — the result is gamma exposure (GEX): each strike's contribution to that dealer book from lesson 4.

Now the bars have a sign, and the map has turned into a forecast of behavior. The green nodes are strikes where dealer hedging will brake the price; the largest of them (the GEX wall, here 6100) is both a brake and a magnet. The purple nodes below are zones where hedging pushes the move along instead: let price fall in there, and dealer selling will start to accelerate it. And the yellow line is zero gamma — the price at which the sign of the whole book flips: above it the market lives in the calm long gamma regime, below it in the nervous short gamma one. One glance at the profile and you know where the market will be sticky and where it will be slippery.

Here it is worth pausing to be honest about what this picture rests on. OI reports how many contracts are open, but not who stands on which side — we warned about this blindness back in lesson 2. To compute the dealer book, the analyst is forced to assume: usually, that dealers stand opposite clients in every position, and that clients behave typically (buying puts for protection, selling calls against portfolios). In a calm market these assumptions run close to the truth, and the profile works. But it is an estimate built on top of a guess — remember that slack; it will play its part later in our story.

Expected move: a corridor made of IV

The last exhibit of the era is the simplest of all. From implied volatility (lesson 2) it follows directly how large a move the market considers normal before expiration: IV is the width of the bell curve, restated as an annualized percentage, and it can be projected onto any horizon. The result is the expected move: "into Friday the market is pricing plus-or-minus forty points." On the chart it is drawn as a corridor around price: the inner boundaries mark the move the market believes in with a probability of about two thirds (one sigma), the outer ones — near certainty (two sigmas). Price leaving the corridor is an event: the market is moving harder than it expected of itself.

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And that is the whole arsenal of the first era: the OI profile, the walls, max pain, the GEX profile with zero gamma, the expected move. We packed it into four indicators — they are already running for ATAS users on CME futures — and the next lesson is devoted to exactly that: what each one shows, how it is read, and which questions come up about it most often.