0DTE refers to options with zero days remaining to expiration — they expire at the close of the current trading session. The CBOE introduced daily SPX expirations in 2022, and 0DTE volume now routinely exceeds 40% of total SPX options volume, materially changing intraday market structure.
Why 0DTE matters for gamma
Gamma concentrates near the money as expiration approaches. For 0DTE options, gamma is enormous and decays minute by minute. This produces two distinctive intraday patterns: violent moves through near-the-money strikes (because dealer hedging amplifies the move once gamma collapses past the strike), and tight late-day pinning to the highest-open-interest strike (because charm + positive aggregate gamma collapse delta to a neutral position at expiration).
ChartGEX merges Schwab's real-time 0DTE feed with CBOE's 15-minute consolidated chain so 0DTE gamma is tracked with the freshness it requires. The gamma flip is re-snapshotted hourly for 0DTE because it can move dramatically during a single session.