Sergey Brin Tops $100 Million in Spending Against California Billionaire Tax

Google co-founder Sergey Brin has now committed more than $100 million to efforts opposing California’s proposed billionaire tax, after contributing another $20 million to Build a Better California, according to a new filing.

Brin, whose fortune is estimated at $267 billion, could face an estimated $13.3 billion tax bill if Proposition 40 takes effect. The measure would impose a one-time 5% tax on the net worth of billionaires who were California residents on Jan. 1, 2026.

California billionaire tax heads to voters

Proposition 40 is expected to affect roughly 200 billionaires and could raise tens of billions of dollars over several years. Most of the revenue would be directed toward health care programs, including Medi-Cal, as California prepares for reductions in federal health funding.

Brin is not the only prominent technology billionaire whose California ties have drawn attention during the tax debate. Meta founder Mark Zuckerberg reportedly purchased a $170 million mansion near Miami this year. At the same time, former Uber CEO Travis Kalanick, venture capitalist Peter Thiel and Brin’s fellow Google co-founder Larry Page have also left California.

Gov. Gavin Newsom opposes Proposition 40, citing concerns about wealthy residents and businesses leaving the state. He has instead advocated for a national billionaires’ tax and criticised strategies that allow wealthy individuals to borrow against stock holdings while reporting little taxable income.

Silicon Valley divides over Proposition 40

Build a Better California has proposed opposing ballot measures that could restrict the introduction of new taxes and potentially block Proposition 40. California voters will decide the billionaire tax in November.

Nvidia co-founder and CEO Jensen Huang has taken a different position. Huang, who could owe roughly $8 billion under the proposal, told Bloomberg in January that he was comfortable with the potential tax.

“We chose to live in Silicon Valley, and whatever taxes they would like to apply, so be it. I’m perfectly fine with it.”

Brin’s latest contribution, meanwhile, brings his spending against the proposal above $100 million, making him one of the most financially committed opponents of California’s billionaire tax as the November vote approaches.