Sam Altman’s Startup Portfolio: Billion-Dollar Bets Revealed in the Musk vs. OpenAI Trial

In the ongoing Elon Musk vs. OpenAI lawsuit, OpenAI CEO Sam Altman took the stand in mid-May 2026 and faced intense scrutiny over his personal investments. Musk’s legal team presented a list of companies in which Altman holds stakes — many of which have business ties to OpenAI — raising questions about potential conflicts of interest.

Altman has no direct equity in OpenAI itself, yet these investments have propelled him into billionaire status. Forbes now estimates his net worth at more than $4 billion (up from a prior $3.5 billion figure), largely thanks to his venture bets in AI infrastructure, energy, biotech, fintech, and beyond.

The trial has given the public an unusually detailed look at Altman’s portfolio. Here’s a breakdown of the key startups he has backed, their performance, and how they intersect with OpenAI.

Star Performers with OpenAI Connections

Helion Energy — The crown jewel of Altman’s holdings.

The nuclear fusion startup aims to build clean, limitless power plants. Altman first invested in 2015 (befriending the founders early) and now owns roughly one-third of the company. His stake is valued at about $1.65–1.7 billion, based on Helion’s latest valuation of over $5.4 billion.

The company has no revenue yet, but the hype around fusion — and OpenAI’s massive energy needs — has driven explosive growth. OpenAI signed a deal with Helion for future power purchases to fuel its data centers, and Altman recused himself from negotiations (even stepping down from Helion’s board in March 2026 to avoid conflicts). This single investment accounts for a huge chunk of his wealth.

Stripe — Fintech giant for online payments.  

Altman’s stake here is worth around $633 million. Stripe powers payments for countless companies, including likely OpenAI itself. The company is valued at roughly $159 billion in recent rounds, making this a solid, high-profile holding in Altman’s book.

Retro Biosciences — Anti-aging biotech play.  

Altman personally led a massive $180 million seed investment when the company launched in 2022.

Retro focuses on reprogramming cells to fight aging. OpenAI collaborated with Retro on AI-driven protein engineering for stem cell research (using models to redesign Yamanaka factors with dramatic efficiency gains).

Altman’s current stake is valued at $258 million. While still early-stage, the scientific progress and AI synergy make this a high-upside bet aligned with Altman’s long-term interests in longevity.

Reddit — Social platform turned AI data partner.

Altman sold his entire stake by the end of 2025. At Reddit’s 2024 IPO, his shares were worth over $600 million. By late 2025, Reddit’s stock had roughly quadrupled from IPO levels, delivering Altman a handsome exit (likely well north of $600 million in realized gains). OpenAI struck a content-licensing deal with Reddit for training data, adding another layer of synergy.

Other Notable Holdings

– Cerebras (AI chipmaker): Altman holds a relatively small ~$3 million stake. The company just completed one of 2026’s biggest IPOs, raising billions at a multi-billion-dollar valuation (with strong demand driven by AI compute hunger). OpenAI signed a major multi-year compute deal with Cerebras worth up to $10 – 20 billion in capacity. Even a tiny slice has upside in the red-hot AI hardware space.

– Lattice (formerly Degree): AI-powered HR and people-management platform. Exact stake size is undisclosed, but the company is a multi-billion-dollar unicorn. Notably, it was co-founded by Altman’s brother, Jack Altman (who stepped down as CEO but remains involved). Lattice helps companies with performance, hiring, and culture — tools increasingly relevant in the AI era.

– Humane: AI hardware startup founded by ex-Apple engineers. They launched the AI Pin wearable a couple of years ago, but sales have been underwhelming. Altman invested early; it’s a higher-risk hardware bet in the consumer AI space.

– Software Applications (software.inc): Early-stage AI software developer. Altman joined other investors in the seed round. The company’s sleek, unconventional website hints at innovative AI tools — still very much a moonshot.

– Formation Bio (formerly Trialspark): AI-driven drug development platform. Altman’s stake is around $19 million. The company uses AI to accelerate clinical trials and pharma R&D, another area where OpenAI’s tech could provide an edge.

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How Successful Is the Portfolio Overall?

Altman’s approach is classic “ecosystem investing”: he bets on the infrastructure, energy, data, hardware, and biotech layers that power (and benefit from) the AI boom he helps lead at OpenAI.

Not every bet has been a home run — Humane’s consumer device struggled, and many of these companies are still pre-revenue or early—but the winners (Helion, Stripe, Reddit exit, Cerebras IPO momentum) have more than offset the risks.

Critics in the trial and on Capitol Hill have flagged potential self-dealing, but Altman has consistently said he recuses himself from relevant OpenAI decisions. Supporters point out that his investments predate many of the partnerships and reflect his long history as a YC president and angel investor.

Verdict? This is a unicorn-heavy portfolio built on deep domain conviction. From fusion reactors that could power the AI future to reprogramming human cells against aging, Altman isn’t just talking about transformative tech—he’s funding it. Whether you’re bullish on AI or not, his track record shows one thing clearly: when Sam Altman invests, the upside can be astronomical.