Anthropic and OpenAI IPO Dates and Valuations: Forecasts and Odds

This page is the standing forecast on when Anthropic and OpenAI go public and at what price, last re-run on October 26, 2026, the day Anthropic's S-1 went public (OpenAI's first-day market cap is from the October 16 re-run); the full company models behind it are in our Anthropic forecast (revenue, compute, Mythos timing) and OpenAI forecast (revenue, losses, and the step-change bet).

tldr Anthropic lists first: median date November 24, 2026, at a median first-day market cap of $1.81 trillion. OpenAI follows around March 2028, at a first-day cap of $1.70 trillion at the median. In June these looked like a near-tie in valuation separated by one quarter in timing. Now more than a year separates them, after Sam Altman ruled out a 2026 listing and OpenAI opened talks on a private round at $1.4 trillion, and the valuation gap is about $110 billion.

When is the Anthropic IPO?

Anthropic's June 1 confidential filing started a procedural clock, and on October 26 the S-1 went public, which puts the roadshow 15 days out at the earliest. Among 22 large US IPOs since 2019, the median time from public filing to pricing was 27.5 days; SpaceX took 22. Press reports point at a Thanksgiving-week debut with Goldman Sachs and Morgan Stanley leading. My re-run pricing distribution has a p10 of November 18, 2026, a median of November 24, 2026, and a p90 of February 15, 2027, pulled in from May 14.

Prediction markets moved further on the filing than my forecast did. Polymarket puts, as of October 26, about 88% on an Anthropic listing by November 30 and about 95% by year-end, up from 55% and 70% on October 16; my curve has about 57% and 79%. The SEC review is no longer the friction. Gross-versus-net revenue accounting was expected to be the question reviewers spent the most time on, and the S-1 kept gross recognition unchanged through five amended drafts. What keeps my tail longer than the market's is the third-quarter amendment the filing still needs, valuation talk that has slipped from $2 trillion to $1.5 trillion, and a Pentagon supply-chain-risk designation that is still live, upheld 2-1 by the D.C. Circuit on September 25 with Anthropic seeking rehearing (CNBC). None of that blocks a listing. Any of it can move the date.

When will OpenAI go public?

OpenAI filed on June 8 and then immediately played it cool: "We have not decided on timing yet; it may be a while… this gives us the option to go public sooner if that ends up being best." Polymarket prices a 2026 OpenAI listing around 3% as of October 26. CFO Sarah Friar has since told employees OpenAI "will be a public company in 2027," if not sooner (CNBC). Then on September 12 Sam Altman ruled out 2026, saying "right now would be an ill-advised moment to go public" (Techzine), and in October Bloomberg reported OpenAI in talks to raise $30 billion or more at a $1.4 trillion pre-money valuation (The Next Web). The October 16 re-run moved the median out to March 15, 2028, and the October 26 re-run held it there.

Anthropic is the one behaving like a company that intends to list. It picked lead underwriters within 48 hours of filing, and it has a competitive prize to capture: first pure-play frontier AI stock. Polymarket gives Anthropic 96% odds of beating OpenAI to the bell as of October 26. My re-run forecast says 93%, up from 89% on October 16 and 63% in June. Scoring that honestly: the market's 83% was closer to where the evidence has landed than my 63% was. I was pricing real doubt about a fast OpenAI counter-move that never materialized.

Anthropic and OpenAI IPO valuations

For Anthropic, I forecast a median first-day close of $1.81 trillion, an 88% premium to the $965 billion Series H that closed on May 28, essentially unchanged from October 16's $1.80 trillion but with a wider range around it. The premium rests on growth, now in audited form: the S-1 shows second-quarter revenue of $11.6 billion with Anthropic's first operating profit, more than 11,900 customers paying $100,000 or more a year, up from 950 a year earlier, and net revenue retention of about 900% (S-1). Third-quarter revenue reached $16.8 billion, up about 45% from the second quarter (CNBC). Talk among prospective IPO investors has cooled, though, from about $2 trillion to about $1.5 trillion after that quarter showed growth slowing (Reuters). That is a valuation for the share sale itself; my $1.81 trillion is a forecast of the first day's close.

The downside scenarios (p10 $1.26 trillion) are no longer about the S-1 review, which left gross revenue recognition intact. They sit in what the filing disclosed. Sequential growth slowed from 144% to about 45%, 80% of first-half revenue was usage-based and largely uncontracted, 5% to 7% of this year's revenue came from customers later found violating usage policy, and the company warns that operating margins may compress as new compute comes online. GAAP operating margin was 8% in the second quarter, which gives public investors a reason to price conservatively. Our full Anthropic forecast puts the 90-day downside near $1.05 trillion. And the mega-IPO pipeline (SpaceX's $75 billion June raise, then at least $60 billion each for Anthropic and OpenAI) is hitting the same pool of institutional capital within a few quarters.

The upside (p90 $2.52 trillion) is the retail scenario, now with a live warning label. SpaceX allocated up to 30% of its offering to retail, triple the usual, demand ran past 4x, and the stock ran to $2.5 trillion before giving the entire scarcity premium back within eight weeks. Cerebras popped 68% on day one in May. There is exactly one pure-play frontier-AI equity coming to market first, and scarcity at trillion-dollar scale now has exactly one precedent to price against, which cuts both ways.

For OpenAI, the re-run median is $1.70 trillion against a March private mark of $852 billion, up from $1.13 trillion on August 29. The near-tie I flagged in June came apart in August, and this month it mostly closed: Anthropic's median barely moved while OpenAI's rose, taking the gap between the two first-day medians from roughly $690 billion to about $110 billion, as OpenAI's listing moved out to 2028 and the reported talks at $1.4 trillion gave it a higher private anchor. The later listing still compounds more revenue under the number, but the market it lists into now has a worked example of what happens when growth arrives with a $25 billion half-year cash burn attached.

I'd also distinguish day one from day ninety, for OpenAI especially. Our full OpenAI forecast puts the expected 90-day post-IPO market cap at $1.77 trillion, against the $1.70 trillion first-day median here. The two are built differently: the first-day figure is an unconditional median, the 90-day figure a probability-weighted blend across the step-change scenarios, so they are not directly comparable. Ninety days is long enough for institutional models to digest the loss line, which FutureSearch now estimates at $63 billion GAAP for 2026 against the widely cited $14 billion non-GAAP figure.

So the race, as I now see it: Anthropic prices first, most likely between late November and mid-December, at a meaningful premium to its last private round, and OpenAI follows more than a year later. On day one, public markets will price the AI race directly for the first time. The following ninety days will be about cash discipline, because SpaceX just taught this market to check.

The full financial models behind each company are in our Anthropic forecast and OpenAI forecast.

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