Anthropic’s S-1 reveals two areas where OpenAI could have the upper hand, experts say

Now that Anthropic’s S-1 is public, it provides a natural comparison point to its rival OpenAI, if and when the latter eventually files its IPO prospectus (likely sometime in 2027).

Analysts have been poring over Anthropic’s filing this week, and so far are already expecting OpenAI’s version to tell a different financial story. Specifically, it could have two potential advantages over Anthropic. The first is in the revenue growth rate. Second, is the diversity of the business, specifically OpenAI’s consumer business.

In the first six months of 2026, Anthropic’s revenue hit $16.3 billion, a 1,300% year-over-year increase—just five years after its founding in 2021. That’s the fastest growth rate among multiple other eye-popping growth rates the company has seen in recent years. In 2023, Anthropic’s revenue was $41 million, and in 2024 it grew 841% to $386 million. in 2025, its revenue jumped again to $4.6 billion, up 1,088%.

“A company hitting this kind of scale this quickly is unprecedented,” Aman Verjee, General Partner and Founder of Practical Venture Capital, told Fortune . Others we spoke to called it “stunning” and “extraordinary.” The consensus is the growth rate is potentially historic.

But investors—and Anthropic itself—don’t expect the trend to continue. “We do not expect our revenue will continue to grow at comparable rates, and we cannot assure you that it will continue to grow at all,” Anthropic’s S-1 reads. The company attributes its ultra-fast growth rate to “early-stage adoption dynamics, the nascency of the AI market, and rapid initial customer expansion,” and notes that it “may not be sustainable over time, and may decline significantly and more rapidly than we anticipate” as the market matures.

We’re already seeing evidence of that slowing. Although the S-1 does not include Anthropic’s third-quarter results, it mentions that revenue was 86-times its Q4 2024 revenue—a sneaky detail spotted by Fortune ‘s AI editor Jeremy Kahn . Since Q4 2024 revenue was $197 million, that implies its Q3 2026 revenue was roughly $16.9 billion. That’s a 47% quarter-on-quarter increase from Q2 to Q3, a sharp drop from its 132% increase between the fourth quarter of 2025 and Q1 2026, and then a 144% increase between Q1 and Q2 2026.

OpenAI’s revenue growth, meanwhile, seems to be picking up steam (from what we can surmise from leaks and executive comments), and sources are expecting its S-1 will reveal accelerating growth on the top line. In August, its CFO Sarah Friar told investors the company now makes more money on enterprise customers than consumers, CNBC reported . Perhaps more concerningly for Anthropic, software engineers are increasingly using OpenAI’s models after a series of price cuts have made them among the most affordable on the market, The Information reported this week.