Trading SPX and Index Options Positioning
Index options carry the deepest open interest available, which makes index positioning data the most reliable positioning data a trader can read.
Why is index positioning more reliable than single stock?
Index option chains carry vastly larger open interest concentrated on standard strikes, so dealer hedging flow is large relative to the underlying liquidity. On a single stock the hedging flow is usually too small to move the share price in any observable way.
How does SPX differ from SPY for positioning?
SPX contracts are cash settled, European style, and roughly ten times the notional size of SPY contracts. SPX therefore attracts institutional positioning while SPY attracts a broader retail mix, so the two chains frequently show meaningfully different level structures on the same trading day.
Should a trader watch both SPX and SPY levels?
The Obsidian desk watches both chains and treats agreement between the two as a strengthening signal. When SPX and SPY levels align at the same index equivalent price, that level carries considerably more weight than either chain would justify alone.