OPEX & the gamma unwind
What happens to positioning when a huge block of gamma expires.
At monthly OPEX, a large share of open interest expires at once. All the gamma tied to those contracts, and the hedges pinning price to their strikes, vanishes after the close. This is the gamma unwind. With those hedges gone, price is often freer to move in the sessions that follow.
Before expiry: pinning
Into the expiry, concentrated gamma pins price to high-OI strikes and suppresses volatility — the market often goes quiet and coils.
After expiry: release
The post-OPEX window
Once the pinning gamma expires, the suppression lifts. The days after monthly OPEX are statistically more volatile — price is freed from the strikes that held it, and a new positioning cycle begins. Plan for range expansion, not continuation of the pre-OPEX calm.