OI vs GEX: what's the difference?

Open interest (OI) and gamma exposure (GEX) measure different things. OI tells you how much positioning sits on a strike. GEX tells you how reactive the dealer hedge is at that strike. High OI and high GEX usually travel together, but not always — and the cases where they diverge are exactly the cases where reading only OI misleads you.

What OI is

OI is the number of open option contracts at a given strike and expiry. On Deribit, every contract represents 1 BTC or 1 ETH. OI ticks up when a new buyer and a new seller open a position; it ticks down when an existing position closes.

It's a level, not a flow. A million contracts of open interest doesn't tell you whether they were bought today or two months ago; it doesn't tell you whether the buyer is long or short delta. It's a count, plain and useful.

What GEX is

GEX weights every contract by its gamma — the rate of change of delta per unit move in the underlying. Gamma is highest for at-the-money options near expiry, and falls off sharply for OTM or far-dated options.

So GEX = OI × gamma per contract × sign of the dealer's net position. Two strikes can hold the same OI and produce very different GEX numbers.

The classic case where OI lies

Take a 30-day BTC option with spot at $100k. Compare two strikes:

  • 100k strike (ATM, 30 DTE): 5,000 contracts of OI. Gamma per contract is high — let's say 0.00010. Total dealer gamma here is large; one big rally and the dealer hedge has to move a lot.
  • 150k strike (deep OTM, 30 DTE): 5,000 contracts of OI. Gamma per contract is near zero — 0.000005. Total dealer gamma here is tiny; even a 5% rally barely shifts the hedge.

Identical OI. Wildly different GEX. The ATM strike has roughly 20× the hedging impact of the deep-OTM strike, even though both show the same column height on a pure OI chart.

When to read which

  • OI answers: where is the biggest positioning concentration? Useful for spotting max-pain candidates and identifying strikes that might cap range pre-expiry through sheer mass.
  • GEX answers: where will the dealer hedge actually move price when spot wobbles? Useful for thinking about volatility regime and short-term intraday pressure.

The dashboard lets you toggle the strike-bar chart between "OI" and "GEX" views. Toggling reveals the difference visually: the OI view tends to be flatter across strikes; the GEX view collapses toward whatever's near spot and near expiry.

Caveats

  • Both metrics are snapshots of public positioning. Private OTC blocks don't show up.
  • Gamma is IV-dependent. A vol spike inflates GEX even if OI doesn't move.
  • The dealer-sign assumption (short calls, short puts) is empirical, not guaranteed. See the "What is GEX?" page for that nuance.