Anthropic confidentially files its S-1 first—but the IPO race with OpenAI is just beginning

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 kicked the company’s valuation up to near-one-trillion—was so intense that it facilitated concerns about financial shenanigans across the private markets, looking to particularly capitalize on both AI FOMO and Anthropic FOMO. There is also some speculation that if Anthropic makes it to the public markets first, it could dampen demand for its less profitable rival. That’s the chess match aspect that’s undoubtedly playing out behind the scenes. 

A few vital caveats, the most important of which is: A confidential S-1 is still a maybe. We have no real numbers yet, and timing remains touch-and-go. (I’ve seen many confidential S-1s go nowhere at all. The filing can be withdrawn at any time, and sometimes the public never hears about it.) So, everything has an asterix for now; Anthropic could go public this summer, this fall, or never. 

Nevertheless, it’s very much a signal, and one the company wants to send loud and clear, given its own blog post on the filing. To me, it seems the signal is this—that Anthropic intends to beat OpenAI to the public markets. Seemingly, they’ve indeed beaten OpenAI to the confidential filing, which means the race is on, though very much undecided. 

Now, it’s OpenAI’s move. They could motor to file, and try to leapfrog Anthropic this summer. And if I had to guess, how SpaceX fares will be a factor too (though how much is unclear—Elon Musk market logic seems to have its own rules of physics). 

We may already know quite a bit about Anthropic, but if the company continues following the IPO path, we will soon learn a lot more.