Why 0DTE Volume Exploded: The Market Structure Behind Same-Day Options
In under a decade, same-day options went from a Friday-only quirk to the majority of SPX options volume. That was not an accident of retail enthusiasm. It was the result of a specific market-structure change, the rollout of daily expirations, meeting expanded retail access and a self-reinforcing dealer-hedging feedback loop. Here is the actual mechanism behind the explosion, and what the numbers do and do not say.