Key Takeaways
- • Family offices made 42 direct investments in September, down from 52 in August, according to data provided exclusively to CNBC by private wealth intelligence platform Fintrx.
- • Hillspire, the personal investment firm of former Google CEO Eric Schmidt, participated in a three billion euro (about $3.4 billion) Series D for French AI startup Mistral.
- • Stanley Druckenmiller's Duquesne Family Office participated in a $500 million Series A for Fab2 and a $250 million Series D for Precision Neuroscience.
- • Centaurus Capital, led by John Arnold, and the John Doerr family office led a $135 million Series B for geothermal startup Mazama Energy, with Bill Gates' private venture firm also participating.
- • Clean energy accounted for five of the month's family office transactions, with Mazama's Oregon pilot reaching 629°F, which the company says is the hottest engineered geothermal system on record.
Summary
Family office deal activity slowed in September, with 42 direct investments in companies, down from 52 the prior month, according to data provided exclusively to CNBC by Fintrx. Although the number of checks declined, ultra-wealthy family investment firms continued to place large bets in late-stage startup financings.
The most prominent transaction was Hillspire's participation in a three billion euro (about $3.4 billion) Series D for Mistral, the three-year-old French company that builds artificial intelligence models, including chatbots, coding assistants and freely available open-weight models. Hillspire is the personal investment firm of former Google CEO Eric Schmidt.
Stanley Druckenmiller's Duquesne Family Office also took part in two rounds that month: a $500 million Series A for Fab2, which manufactures small semiconductor factories, and a $250 million Series D for Precision Neuroscience, which develops brain implants that record neural signals to let users control digital devices.
Clean energy remained a focus, representing five of the month's transactions. Centaurus Capital, the investment vehicle of John Arnold, and the namesake family office of John Doerr led a $135 million Series B for Mazama Energy, a geothermal startup. Bill Gates' private venture capital firm also participated. Arnold and Doerr, who made their fortunes in hedge funds and venture capital respectively, have backed several clean energy startups this year.
Mazama drills into extremely hot rock and circulates water through engineered fractures to bring heat to the surface for carbon-free electricity, a method the company says lowers power costs by generating more energy from fewer wells. In 2025, its Oregon pilot site reached 629°F, which Mazama says is the hottest engineered geothermal system on record. CEO Sriram Vasantharajan said the proof of concept demonstrated a clear path to commercialization and was key to attracting top investors, adding that the Oregon site is already capable of producing 10 gigawatts of energy. He described the challenge as one of engineering rather than science.
The most prominent transaction was Hillspire's participation in a three billion euro (about $3.4 billion) Series D for Mistral, the three-year-old French company that builds artificial intelligence models, including chatbots, coding assistants and freely available open-weight models. Hillspire is the personal investment firm of former Google CEO Eric Schmidt.
Stanley Druckenmiller's Duquesne Family Office also took part in two rounds that month: a $500 million Series A for Fab2, which manufactures small semiconductor factories, and a $250 million Series D for Precision Neuroscience, which develops brain implants that record neural signals to let users control digital devices.
Clean energy remained a focus, representing five of the month's transactions. Centaurus Capital, the investment vehicle of John Arnold, and the namesake family office of John Doerr led a $135 million Series B for Mazama Energy, a geothermal startup. Bill Gates' private venture capital firm also participated. Arnold and Doerr, who made their fortunes in hedge funds and venture capital respectively, have backed several clean energy startups this year.
Mazama drills into extremely hot rock and circulates water through engineered fractures to bring heat to the surface for carbon-free electricity, a method the company says lowers power costs by generating more energy from fewer wells. In 2025, its Oregon pilot site reached 629°F, which Mazama says is the hottest engineered geothermal system on record. CEO Sriram Vasantharajan said the proof of concept demonstrated a clear path to commercialization and was key to attracting top investors, adding that the Oregon site is already capable of producing 10 gigawatts of energy. He described the challenge as one of engineering rather than science.
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