TLDR: movement in the $VIX and VIX options yesterday far outstripped moves in the SPX. there's information about market fragility here that we should be mindful of. the VIX and SPX are negatively correlated. run the regression and it's on the order of -80%. but the slope of the regression (change in VIX per change in the SPX) is time varying. we have periods when the VIX moves a ton relative to the SPX move (Feb'18 volmagedon). in contrast, 2022 brought an extremely dull VIX, muted reactive to moves in the SPX. yesterday, especially from 12:30 to 1:30pm, both the VIX and $VVIX moved a great deal relative to the move in the SPX. I show this below (thank you, Claude). typical VIX beta (% move in VIX per 1% move in the SPX) has been around 7. yesterday it reached on the order of 50. from 12:30 to 1:30, SPX down just 60bps...VIX up 29% (50x)... talking my own thinking here, but there is no security in markets better equipped (at a low price) to hedge a near term crash than a short-dated out of the money call option on the VIX. this is what got really bid yesterday. the Oct 25 call (expires Wednesday) went from being worth 6 cents in the morning to more than $1 a few hours later. it exploded not just because the VIX rose so much, but because "vol of vol" surged as well. no security is more "spot up, vol up" than the VIX itself. it will be interesting to see if this was a one-off or indicative of a larger shift in behavior where investor seek to cover deep left tail risk.