Billionaire Backer Sergey Brin Leads $102 Million Fight Against California’s One-Time Wealth Tax

California voters will decide in November whether Proposition 40 passes, a ballot measure that would levy a one-time 5 % tax on the assets of residents whose net worth exceeds $1 billion. The tax could generate roughly $100 billion, enough to cover the state’s projected $20 billion annual shortfall in Medi-Cal funding. Google co-founder Sergey Brin has contributed $102 million to the anti-tax coalition, making the campaign one of the most expensive political battles in the country.

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Prop 40 is designed to apply to assets—stocks, property, and trusts—rather than income, targeting about 250 California billionaires. The measure was announced in late November 2025, giving wealthy residents only a month to change residency, a restriction architects say makes “severing residency… impossible” (Emmanuel Saez, UC Berkeley). Proponents argue the tax is a response to federal health-care cuts under the One Big Beautiful Bill Act, while opponents warn it could drive job creators out of the state.

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• Sergey Brin – Google co-founder, board member of Alphabet, donor of $102 million to Building a Better California.

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• Building a Better California – Advocacy group funding the “No” campaign and supporting rival initiatives Prop 41 and Prop 42.

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• Peter Thiel, John Doerr, Patrick Collison – Additional billionaire donors.

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• Emmanuel Saez – UC Berkeley professor and architect of the tax.

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• Brian Galle – UC Berkeley professor who helped draft the measure.

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• Robert Lapsley – President of the California Business Roundtable, representing business interests.

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• Brin’s $102 million contribution accounts for the bulk of nearly $100 million in ad time purchased by the opposition, according to AdImpact data.

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• Pro-tax ads have received about $100 000 in funding, a stark disparity.

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• Polls show a divided electorate: a UC Berkeley IGS poll found 48 % support, while a Public Policy Institute of California poll indicated 52 % support after voters read the ballot title.

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• The tax would affect roughly 250 individuals with net worths over $1 billion.

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Brian Galle warned, “Providers in places with vulnerable populations that depend a lot on Medicaid are going to be hit especially hard.” “Providers in places with vulnerable populations that depend a lot on Medicaid are going to be hit especially hard,” — Brian Galle, another professor at UC Berkeley Governor Gavin Newsom, in a Substack post, expressed sympathy for the tax’s goals but advocated for a national minimum tax on billionaires instead of a state-specific measure. Robert Lapsley argued, “We already have all the highest taxes in the country — gas taxes, income taxes,” and warned that an additional asset tax would drive “job creators… out of here.” “We already have all the highest taxes in the country — gas taxes, income taxes,” — Robert Lapsley, president of the California Business Roundtable Brin, recalling his 1979 escape from Soviet socialism, told The New York Times,

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The outcome of Prop 40 will shape California’s fiscal future and could set a precedent for wealth-tax initiatives nationwide.

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