1: First of, you are correct SPY's volume is a bit concerning. SPY mostly represents ETF purchase, so, this is indeed an indication that less volume has been traded on the actual index positions
2: At the same time, the derivative volume on SPX is quite consistent to last year's behavior. Typically, SPX volume reflects the trading on ES futures, and this is largely driven by dealer hedgeing as well as institution players positioning their portfolios.
So, this could mean one of the two things
A: instituions are ahead of retails this time and after this big spike, market pulls back a small bit, and retails FOMO money continues to pour in and SPX goes to 8100 eventually (in other word, SPY volume will evnetually catch up with SPX volume)
OR
B: instituions will take this chance to sell to retails and pull the plug eventually. The bigger volume on SPX means they are hedging their positions while less not committing to SPY (the actual stock and index)
I dont know whether it is A or B. Will need to see how market pulls back to know it
