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........

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