If you've built anything involving options data, you've probably noticed that "SPX 0DTE" is everywhere on fintwit, Discord, and trading blogs. The thing most guides gloss over is that plain SPX doesn't actually have same-day expirations every day . What everyone means when they say "SPX 0DTE" is SPXW — a different ticker with different settlement and different Greeks behavior.

I build an options analytics API, and the distinction matters enough that every developer touching options data should understand it before their dashboard lies to them.

SPX, SPXW, XSP — the one that's actually 0DTE

Three S&P 500 option tickers trade on Cboe. Only one gives you same-day expirations every trading day:

Ticker Listing cadence Settlement Contract size

SPX Third-Friday AM expirations AM cash-settled $100 × index

SPXW Mon/Tue/Wed/Thu/Fri PM expirations PM cash-settled $100 × index

XSP Mon-Fri PM PM cash-settled $10 × index

Plain SPX has no Monday, Tuesday, Wednesday, or Thursday expirations.…