You should not trust me, but here's my understanding. I wish there was a really good writeup somewhere to explain this authoritatively but I'm not sure there is one. Would also love to see one. Frankly vanguard should do it.

VTSAX (and VTI) follow the CRSP index. This is float-adjusted but they likely will be fast tracked (these are two separate rules in how this index chooses to weight things and participate in new stocks). At ~5% float, these companies will be in the 50-100B range. So under all those assumptions, they'll be bought quickly but represent less than 1% of VTSAX (until they float more shares on the public market).