What it means
0DTE (zero days to expiration) options are contracts expiring the same day they're traded. SPX 0DTE was made possible by the Tuesday/Thursday weekly expiration cycle (added 2022) combined with the original Monday/Wednesday/Friday cycle — meaning SPX has 0DTE options trading every business day. Volume in SPX 0DTE has grown to ~50% of total SPX options daily volume. The intraday flow concentration in 0DTE has created entirely new intraday market dynamics.
Why it matters
0DTE flows have changed intraday SPX behavior dramatically since 2022. The 'V-shaped intraday reversal' pattern that became common is largely driven by 0DTE dealer gamma flipping during the session. 0DTE positioning at session open vs session close can flip dealer gamma exposure by $2-5 billion intraday — a structural force that didn't exist pre-2022. Trading SPX intraday without understanding 0DTE flows is trading half-blind.
How to use it
Track 0DTE positioning at session open: net call vs put delta, gamma concentration by strike. Use providers (SpotGamma, Tier1Alpha) for real-time decomposition. Major call-heavy 0DTE positioning at session open = dealer gamma negative on calls = upside acceleration if rally; reverse for put-heavy.
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