0DTE: the gamma that lives and dies inside your session

What has changed

SPX options now expire every weekday. 0DTE options (zero days to expiration), bought in the morning and dead at the bell, made up 65% of SPX volume in May 2026, about 3.1 million contracts per day. This is no longer a niche market: it is the core of the options flow on the index.

For a flow trader, 0DTE has three properties that make it a player apart:

1. Its gamma is enormous near the money. At zero time to expiration, the gamma of an at-the-money option explodes. A 0DTE strike close to price concentrates more hedging need than a monthly strike ten times larger in open interest.
2. Its gamma is localized. A few points away, there is almost nothing left. 0DTE creates gamma pockets around the active strikes, not a background structure.
3. Its gamma dies at 4:00 pm New York. Everything hedged during the day unwinds in the last hours, then disappears. Tomorrow, the 0DTE book starts from zero.