What is OpEx?
OpEx is options expiration — the dates when listed options contracts expire, headlined by the monthly expiration on the third Friday and the larger quarterly expirations in March, June, September, and December when index futures and options expire together. OpEx matters to the broader market because expiration removes a large block of options positioning at once, and the dealer hedges held against those options are unwound or rolled with it — a mechanical flow event that recurs on a fixed calendar.
Why does the market often pin into OpEx?
Gamma is highest for options near the money and close to expiration. In the final sessions before OpEx, the gamma concentrated at big strikes peaks, and where dealers are long that gamma their hedging — selling strength, buying weakness — pulls price toward the heavily-populated strikes and holds it there. This is the pinning effect: ranges compress and price gravitates to large strikes not because of news, but because hedging pressure around those strikes crescendos into expiration.
What happens after OpEx?
The positioning that enforced the range disappears. When the expiring options roll off, the gamma that concentrated at those strikes — and the hedges against it — vanish, leaving the market with less stabilizing flow. This is why the sessions after a large expiration often show expanded ranges and directional moves: the pin is released, and price can travel until new positioning builds. The week after quarterly OpEx is a classic window for volatility regime shifts.
Is every OpEx bullish or bearish?
Neither — OpEx is a positioning event, not a directional signal. What it changes is the freedom of the market to move, and the direction after expiration depends on what positioning remains and what flows arrive next. Calendar heuristics like “OpEx week is bullish” come and go; the durable fact is structural: expiration removes gamma, and removed gamma means less pinning and wider potential ranges.
How do traders track OpEx positioning?
By measuring how much gamma expires and where it sits: which strikes hold the large concentrations, how much of total gamma rolls off at this expiration, and whether dealers are long or short the gamma that remains after. That last question is the one raw open interest can’t answer — it requires estimating who holds the positions, which is what SpotGamma’s SGOI does. Combined with gamma exposure levels like the call and put walls and the real-time hedging flow in HIRO, it shows how much of the market’s current structure is scheduled to disappear on Friday — and what’s left standing after.
Last updated: August 2026 — Published by SpotGamma. Related: call walls and put walls and negative gamma.