So it’s well known that Y Combinator owns some stake in OpenAI. But how big is that stake? This seems like devilishly difficult information to obtain. I asked around and a little birdie who knows several OpenAI investors came back with an answer: Y Combinator owns about 0.6 percent of OpenAI. At OpenAI’s current $852 billion valuation (https://openai.com/index/accelerating-the-next-phase-ai/), that’s worth over $5 billion.

— John Gruber (https://daringfireball.net/2026/05/y_combinators_stake_in_openai), Y Combinator’s Stake in OpenAI

Tags: openai (https://simonwillison.net/tags/openai), y-combinator (https://simonwillison.net/tags/y-combinator), ai (https://simonwillison.net/tags/ai), john-gruber (https://simonwillison.net/tags/john-gruber)