I don’t want to believe for a second anyone would walk away from Silicon Valley because of being taxed. The impact on the calculus of reward simply doesn’t make sense. On the other hand I am always surprised by people and the strange things we do.
Most people, by count, of course would not leave because of the wealth tax currently being proposed in California as it targets just a tiny segment of the population - current estimates are that less than 250 Californians, or less than 0.001%, would pay the currently proposed statewide wealth tax. The other 99.999+% would not (yet) have to pay a wealth tax. However, the <0.001% that (esp. the wealthiest among them) who would pay the wealth tax would be motivated to move.
Unfortunately for California about 40% of the total state income tax collected (which accounts for about 65% of the state general fund) is paid by the top 1% of income earners -- which includes those 0.001% who will be motivated to move by a wealth tax (or even merely the threat of one).
The <0.001% number appears to be based on population _before_ several billionaires moved out before Jan 1, 2026 - likely at least partially motivated by the small, but real, risk of the "billionaire's tax" qualifying for the ballot and passing (and that proposed tax is only "temporary" and is only a total of 5% over three years so isn't nearly as alarming to the wealthy as a "permanent" tax would be). If it looks like this measure will end up on the ballot and have a chance of passing, expect many more to leave. This will, even if it does not ultimately pass, erode the income tax base.
California has rebelled against wealth taxes in the past - most notably by the passage of Prop 13 almost 50 years ago (a property tax is a wealth tax). They are not popular except when the hit "the other guy" -- but "the other guy" is the one most able to avoid the tax.
Wealthy people are typically very flexible as to where they live. They often already own multiple homes and often spend a lot of time out of the state they "live" in. When they move, they are not packing and labeling their own boxes or are likely even present on "moving day". They also are more likely to set up HQ and shop near where they spend a lot of their time. Even if they have family in California, they can still get together with them for Thanksgiving dinner -- either by flying the family to them on their private and chartered jets or by themselves flying to California for the weekend on one of their jets. They can conduct most business very efficiently remotely and often do so now to a significant extent.
It only takes a few to leave to tank the California budget - likely causing the progressive income and wealth taxes to reach deeper and deeper into the upper middle classes as California desperately tries to balance their budget without cutting yet more programs.
Other states are loving this though and will cut tax deals to attract these very billionaires that California are encouraging to leave.
People walk when they don’t make money. You don’t look at Silicon Valley for these types of things. You look at a deprived forgotten town that could had survived were they not squeezed so much