Customers don't predictably re-hedge their deltas, so their impact on the underlying isn't as uniform as dealers'. But they still respond to changes in S&P 500 price and volatility, just like dealers do.
They just tend to do it all at once.
And at bad times.
We're getting pretty close to one of those "bad times."
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With the benefit of understanding daily SPX put flows (NPD) with some granularity, we have a model to overlay atop our understanding of customers' excess vanna exposure (VGR).
A "bad time" is when everyone is overexposed to the same thing. This makes the market fragile.
As you know, an option's delta is not only sensitive to spot price (gamma), but also to volatility (vanna). We've called vanna "gamma's evil twin." She's sneaky.
So you shouldn't be surprised that when vanna [quietly] becomes a relatively larger portion of SPX option customers' delta sensitivity, things can get weird.
After all, when more people are more exposed to vanna, they are more exposed to changes in vol!
S&P 500 (SPX) option dealers hold more and more inventory.
"But what about the other 50%?" you wonder.
Normally, this would be an opportunity for us to plug gamma exposure (GEX).
"Dealer gamma is only getting more important!"
But that's just not true anymore. As dealer inventory gets bigger, and as people model it with increasing accuracy, it actually becomes *less* important.
People figured out that it matters, so it matters less.
Ever since June (at $200/share), Tesla stock has been driven by a perpetual motion machine of hype and call option flows -- nothing more. And everyone knows it.
Here's what not everyone knows:
When a stock joins the S&P 500, it becomes part of a massive volatility complex, which is a terrifying web of arbitrage and pseudo-arbitrage relationships. Tesla will join the index as a top-ten component of a cap-weighted index. It's big.
Its bigness will allow all manner of dispersion, relative value, and market-making traders to begin relying on Tesla's newfound correlation to the index. This will invariably cause arbitrageurs to buy SPX options/vol and sell TSLA options/vol to "close the spread."