Investment firms of ultra-wealthy families, including those of John Arnold and Stanley Druckenmiller, invested in cutting-edge technology such as geothermal energy and brain implants in September. Eric Schmidt's Hillspire participated in a €3 billion Series D round for AI startup Mistral. Druckenmiller's Duquesne Family Office invested in semiconductor factory manufacturer Fab2 ($500 million Series A) and brain implant developer Precision Neuroscience ($250 million Series D). John Arnold's Centaurus Capital and John Doerr's family office led a $135 million Series B round for geothermal energy startup Mazama Energy, with Bill Gates' firm also participating.