Anthropic’s confidential S-1 signals summer AI IPO race could heat up fast

Anthropic was open about its confidential S-1 filing on Monday. The $965 billion AI juggernaut announced the filing—which we cannot yet see—on its blog. It’s a contradiction, but then Anthropic is its own kind of contradiction, a still-young private company we know quite a lot about. The nearly trillion-dollar startup (if it can be called such a thing) has gotten so big that it’s hard to hide in the markets the way a growth-spurting elephant is hard to hide in a zoo. The company—founded in 2021 and helmed by siblings Dario and Daniela Amodei—has seen a historic rise. Back when our AI editor Jeremy Kahn wrote his Fortune cover story on Anthropic in December 2025, the company was valued at $183 billion. One prophetic section: [Dario] thinks Anthropic could surpass OpenAI as the world’s largest AI company by revenue. “I would argue it’s maybe even the most likely world in which our revenue passes theirs a year from now,” he says. Then he pauses before adding, “I think I’d rather have the largest revenue than the largest data center, because one is black [on an income statement], and the other is red. Again, things I’ve had to learn about business: It’s better to make money than just to lose money. What a difference a few months can make. Anthropic’s annualized revenue run rate hit $47 billion in May, and while that’s no guarantee of the future, it is astonishing. It’s dazzling not only for its scale, but for the way that, in half a decade, upstart Anthropic seems to have gotten a leg-up on ChatGPT maker OpenAI (comparatively last valued at $852 billion). One wonders what investor appetite will look like for Anthropic versus OpenAI. Reports have suggested that OpenAI’s financials aren’t as strong as Anthropic’s, and word’s spread that OpenAI shares aren’t as in demand in the secondary market. Meanwhile, competition for Anthropic secondary shares has been rabid, as I’ve previously reported. The relentless demand for Anthropic’s May Series H—which raised $65 billion and k