Aside from becoming a household name with the breakout success of ChatGPT in 2022, OpenAI CEO Sam Altman has long been one of Silicon Valley’s most influential startup investors. Long before generative A.I. captured global attention, Altman built a reputation as a prolific angel investor whose bets helped shape the modern tech landscape, from early stakes in Stripe, Reddit and Instacart to later, high-conviction investments in nuclear energy and longevity science.
Altman’s track record as an early-stage investor was shaped during his time at Y Combinator, where he served as president from 2014 to 2019. In that role, he helped oversee investments in hundreds of startups, several of which went on to become major technology companies. After leaving YC, Altman continued to invest personally in both alumni companies and new ventures.
Over the years, Altman has invested in more than 400 companies through a mix of personal angel checks, his own funds like Hydrazine Capital and Apollo Projects, and partnerships with larger venture firms.
Altman’s 2025 investment activity has centered on startups in A.I.-driven security, biotechnology and nuclear fusion, according to Crunchbase data. These bets reflect not just a desire to diversify across cutting-edge industries, but also to champion “moonshot” ventures tackling some of today’s most complex challenges, from intelligence augmentation and clean energy to breakthroughs in human health.
Here are the startups that Altman invested in this year:
Helion Energy
- Product: fusion power
- Investment channel: personal/angel investing
- Investment: $425 million Series F in January
- Valuation: $5.4 billion
Helion Energy is a nuclear fusion company working to commercialize fusion power as a zero-carbon energy source. The company is building its first fusion power plant in Chelan County, Wash. scheduled to come online in 2028. As data centers and advanced A.I. systems drive a surge in electricity demand, interest in scalable, emissions-free power has grown across the tech industry. Helion is positioning itself to meet that demand with a patented pulsed, non-ignition fusion approach designed to generate electricity directly, without relying on traditional steam turbines. Altman has been one of the company’s most prominent backers for several years, calling Helion in 2021 “by far the most promising approach to fusion I’ve ever seen.” His latest investment came as part of Helion’s $425 million Series F round in January.
MirrorTab
- Product: web security technology
- Investment channel: Altman Capital
- Investment: $8.5 million seed round in February
- Valuation: not disclosed
MirrorTab develops browser-based security tools that protect customer-facing web applications from threats including malware, automated fraud, sophisticated bots and so-called agentic A.I. abuse. MirrorTab uses pixel-streaming technology to prevent untrusted browsers, extensions and scripts from accessing sensitive data or code, without requiring users to install additional software. “Most vendors are focused on enabling A.I.—far fewer are working to restrict it,” CEO and founder Brian Silverstein said at a recent conference. “Effective A.I. security requires knowing when to leverage A.I. and when to block it entirely.”
Campus
- Product: Online educational services
- Investment channel: personal/angel investing
- Investment: $46 million Series B in March
- Valuation: $100 million
Campus is an online, two-year college offering lower-cost accredited degrees taught by professors from institutions including Stanford, Princeton, and Howard University. Students attend live online classes and supplement coursework with A.I.-generated educational tools developed by Sizzle A.I. The school currently offers associate degrees in business administration and information technology, with an optional concentration in applied A.I. focused on business use cases. Altman backed Campus through its $46 million Series B round, alongside investors such as Figma CEO Dylan Field, Palantir co-founder Joe Lonsdale and Shaquille O’Neal. Altman also helps fund the company’s Shaq Scholars Program, which provides financial support to enrolled students.
ConductorAI
- Product: automation software
- Investment channel: Altman Capital
- Investment: $15 million Series A in April
- Valuation: not disclosed
Founded by former Palantir employees, ConductorAI focuses on automating complex government approval and compliance workflows. The company’s software, which has been contracted by the U.S. Air Force, Space Force and the Office of the Secretary of Defense, uses A.I. to review large volumes of policy and regulatory documents. According to Business Insider, ConductorAI has primarily been used to automate security classification, with additional applications in export licensing, International Traffic in Arms Regulations compliance and document review.
Exowatt
- Product: renewable energy
- Investment Channel: angel investing
- Investment: $70 million Series A in April and $50 million in November
- Current valuation: $140 million
Exowatt builds modular power systems designed to deliver large-scale, on-demand energy. Its technology uses Fresnel lenses to concentrate sunlight into thermal energy, which is stored in ceramic bricks that function as batteries for the system’s engine and power generator. While the underlying approach is not new, Exowatt is betting that fresh capital—from Altman, venture firm Andreessen Horowitz and investors including Leonardo DiCaprio—will allow it to manufacture and deploy systems domestically at speed. The goal is to serve data centers facing surging demand for round-the-clock power that is cheap, reliable and low-carbon.
Coco Robotics
- Product: delivery robots
- Investment channel: personal/angel investing
- Investment: $80 million Series B in June
- Valuation: $300 million
Altman was a lead investor in Coco Robotics’ $80 million Series B round in June 2025. The Santa Monica–based startup builds small delivery robots used for last-mile logistics by platforms including DoorDash and Uber Eats. Coco’s robots rely on GPS, LiDAR cameras and A.I. systems powered in part by OpenAI models to navigate dense urban environments and make real-time routing decisions. Since launching in 2020, the company has deployed robots in cities including Los Angeles, Austin, Miami and Helsinki. Expansion has drawn scrutiny, however: in Chicago, more than 800 residents had signed a petition by late November calling for a pause to Coco’s pilot program, citing safety and accessibility concerns.
Arcadia Medicine
- Product: bioengineered psychoactive medicines
- Investment channel: personal/angel investing
- Investment: $9.25 million seed round in October
- Valuation: not disclosed
Arcadia Medicine develops engineered entactogens—psychoactive compounds designed for therapeutic use—to treat conditions such as major depressive disorder, generalized anxiety disorder and substance use disorder. The company creates modified versions of drugs including MDMA, psilocybin and ketamine, aiming to enhance their therapeutic benefits while reducing safety risks to meet medical and regulatory standards.
In October, the U.S. Food and Drug Administration approved human trials for Arcadia’s redesigned MDMA compound, which the company says is non-neurotoxic and allows for flexible dosing. Altman participated in the company’s $9.25 million seed round and has publicly described its work as “an important step toward a potentially transformative psychiatric treatment,” lending early credibility as Arcadia prepares for more advanced clinical trials.
Red Queen Bio
- Product: biosecurity
- Investment channel: OpenAI
- Investment: $15 million seed round in November
- Valuation: $20 million–$25 million
Red Queen Bio is a biosecurity startup that emerged from Helix Nano, an mRNA therapeutics company that applies A.I. to drug development and biological risk assessment. Named after the “Red Queen hypothesis,” which posits that species must continuously adapt to survive against evolving threats, the company aims to build safeguards for advanced A.I. systems at the same pace as their capabilities improve. While Altman did not invest directly in Red Queen Bio, his prior backing of Helix Nano resulted in an equity stake when OpenAI led Red Queen Bio’s November seed round, positioning the startup as part of OpenAI’s broader effort to address biological risks tied to powerful A.I. models.
