[anamax]

Google is public, so the 5% of max(ownership, control) clause doesn't apply.

However, there are a bunch of private unicorns whose founders are subject to the tax even though their ownership is well under $1B.

See Section 50303(c)(3)(C) quoted above.

[VirusNewbie]

It does apply, because Sergey's shares are not the same kind available on the public exchange.