Sam Altman
About Sam Altman
Sam Altman is CEO of OpenAI and led Y Combinator from 2014 to 2019. He is based in San Francisco. He studied computer science at Stanford and dropped out in 2005 to found Loopt, a location-based social app that was part of Y Combinator's first batch. Green Dot acquired Loopt in 2012 for $43.4 million.
In April 2012 he co-founded Hydrazine Capital with his brother Jack Altman. The initial fund was $21 million, and most of it came from Peter Thiel. Altman put about 75 percent of that money into Y Combinator companies. In 2023 Hydrazine launched a fourth fund, and the University of Michigan endowment was its only outside investor.
He joined Y Combinator as a part-time partner in 2011 and succeeded Paul Graham as president in 2014. He became CEO of OpenAI in 2019. He has also held board roles at energy companies including Helion, UPower and Oklo, and he co-founded Worldcoin in 2020. Crunchbase lists 0 companies founded for him, so treat the founder history above as coming from press and Wikipedia rather than Crunchbase.
Crunchbase counts 33 investments for Altman, with 0 lead investments. It lists no exits, although other trackers record some, such as Reddit's 2024 IPO. Dealroom tracks about 150 portfolio companies across his personal and fund investments. Counts differ by source because his activity runs through several vehicles, including Hydrazine Capital, Apollo Projects and Altman Capital.
During his Y Combinator years he backed companies such as Instacart, Docker and Zenefits. He also backed science-heavy companies such as Helion Energy and uBiome. His largest known positions are Helion Energy, Reddit, Stripe and Retro Biosciences. Court filings reported in May 2026 put his disclosed stakes in nine private companies at more than $2 billion as of December 31, 2025, with Helion the largest. He holds no direct OpenAI equity, according to the same reporting.
Crunchbase shows 12 AI investments since 2023. Its AI portfolio includes Software Applications Incorporated, Arkham Intelligence, APEX, Coco, Beacon AI, Red Queen Bio, Limitless AI (formerly Rewind AI), Exowatt, Warp and Induced AI.
Some dated examples:
Software Applications Incorporated raised a $6.5 million seed round in November 2023, per VC Backed. Warp raised a round in June 2023 and Airchat in April 2024, per Crunchbase's activity timeline. Exowatt emerged from stealth in April 2024 with a $20 million seed round led by Andreessen Horowitz and Atomic, with Altman also participating. Exowatt builds energy storage aimed at AI data centers. Red Queen Bio raised a round in November 2025. It works with frontier labs to map AI-enabled biothreats and pre-build medical countermeasures.
A pattern in his portfolio is the physical and resource layer behind AI, such as energy (Helion, Exowatt), payments (Stripe), data (Reddit) and identity (World).
Altman has no published check size. Aggregator averages cover his whole portfolio, including large late-stage rounds, so they do not describe what he writes into a seed round. Crunchbase and the public record show him mostly as a participant rather than a lead.
Stage: his portfolio runs from seed-stage startups to late-stage companies. Hydrazine's early-stage mandate covered life sciences, education, specialty foods, marketplaces, big data, healthcare, consumer networks, enterprise software and connected hardware.
Sectors: AI software, energy (fusion, thermal storage, fission), longevity and biotech, fintech, consumer hardware and supersonic aviation. Third-party analyses describe a recurring preference for hard technology with long time horizons.
What he says he looks for: on his blog he writes that great founders are the key to great startups. The main question he asks himself is whether he would work for the founder, and the second is whether he can imagine them taking over their industry. He says he values rate of improvement over current ability, and he likes founders who are scrappy and formidable at once. He recommends meeting founders in person several times. In his startup playbook he ranks determination, resourcefulness and unstoppability above experience and specific technical expertise.
Geography: he is based in San Francisco and his investments are mostly US-based companies.
- Stripe: online payments infrastructure; early personal investment, with a disclosed stake reported in 2026 court filings.
- Reddit: social media platform; early investor, later listed publicly in 2024. He was also briefly its CEO.
- Helion Energy: nuclear fusion developer; his largest disclosed stake, and he chairs the company.
- Retro Biosciences: longevity company working on cellular reprogramming; reported $180 million commitment.
- Oklo: nuclear fission company; he served on its board and it listed publicly in 2024 through his AltC SPAC.
- Exowatt: thermal energy storage for AI data centers; $20 million seed in April 2024 alongside a16z and Atomic.
- Red Queen Bio: AI biosecurity company; round in November 2025.
- Software Applications Incorporated: AI personal computing software; $6.5 million seed in November 2023.
- Warp: AI-enabled developer terminal; round in June 2023.
- Humane: consumer AI hardware; early investor per press coverage.
- Instacart, Docker, Zenefits: Y Combinator-era investments.
- en.wikipedia.org/wiki/Sam_Altman
- blog.samaltman.com/how-to-invest-in-startups
- playbook.samaltman.com
- lb.crunchbase.com/person/sam-altman/person_overview_investor/timeline
- crunchbase.com/person/f63055a5-a077-f7ad-2ace-9dbbac22a366
- dealroom.co/investors/sam-altman
- startuphub.ai/ai-news/ai-figures/2026/figure-sam-altman-venture-portfo
- capitaly.vc/blog/sam-altmans-investment-portfolio-beyond-openai
AI portfolio
Investing activity
Sam Altman has made 33 investments according to Crunchbase. 12 of those investments since 2023 were in AI companies, including Software Applications Incorporated, Arkham Intelligence, APEX, Coco and Beacon AI.
Deals
Frequently asked questions about Sam Altman
What does Sam Altman look for in a founder?
He says he asks whether he would work for the founder and whether they could take over their industry. He values determination, resourcefulness and fast improvement over experience, and prefers to meet founders in person several times.
What is Sam Altman's check size as an angel investor?
No check size is public. Reported figures for his portfolio mix small seed rounds with very large commitments such as Retro Biosciences, so they do not indicate a typical angel check.
Does Sam Altman invest in AI startups?
Yes. Crunchbase lists 12 AI investments since 2023, including Software Applications Incorporated, Warp, Red Queen Bio, Limitless AI and Induced AI. He also backs energy companies that serve AI demand, such as Exowatt and Helion.
Does Sam Altman lead investment rounds?
Crunchbase lists 0 lead investments for him. In the rounds found, such as Exowatt's seed, he participated alongside a lead investor.
What stage does Sam Altman invest in?
His portfolio spans seed-stage startups to late-stage companies. His AI investments since 2023 are mostly early-stage rounds, such as a $6.5 million seed for Software Applications Incorporated.
How can founders contact Sam Altman?
He publishes essays and startup advice at blog.samaltman.com and is on X and LinkedIn. No public pitch process or intake address was found.
Is Sam Altman an angel investor?
Yes. Sam Altman invests personally as an angel. Crunchbase counts 33 investments.
What AI companies has Sam Altman invested in?
Sam Altman's AI investments include Software Applications Incorporated, Arkham Intelligence, APEX, Coco, Beacon AI, Red Queen Bio, Limitless AI (formerly Rewind AI) and Exowatt.
Where is Sam Altman based?
Sam Altman is based in San Francisco, United States.
How can founders reach Sam Altman?
Founders on Lounge can see Sam Altman's contact details in AI Investor Contacts (paid plans), check for a warm introduction through members who worked with them under Warm Paths, and add Sam Altman to their Investor Pipeline to track the conversation.