What is an IPO? How a company goes public, explained through Anthropic’s listing

Anthropic, the company behind the Claude artificial intelligence (AI) models, is preparing to sell its shares to the public for the first time. If it goes ahead as planned, it’ll be the second largest stock market listing on record, which makes it a useful live example of how an initial public offering (IPO) works.

Below, we go through the process step by step. The Anthropic figures come from the company’s own filings and announcements as of 13 November 2026, and the final terms could still change.

What is an IPO?

An IPO is the first time a private company sells its shares to the public on a stock exchange. Before the IPO, the shares belong to founders, staff and private investors. After it, anyone with a brokerage account can buy and sell them.

Companies mainly go public to raise money by selling new shares, and to give founders, staff and early investors a public market for the shares they already hold. Anthropic says it plans to use the money for general corporate purposes, including computing power and infrastructure.

How an IPO works, step by step

1. The filing. The company files a document called a prospectus with the market regulator. In the US, that’s the Securities and Exchange Commission (SEC), and the form is called an S-1. It sets out the business, its finances and the risks. Anthropic sent the SEC a confidential draft on 1 June 2026 and made its S-1 public on 26 October.
2. The underwriters. Investment banks, known as underwriters, run the sale. They help set the price and find buyers. Anthropic’s filing lists 22 banks.
3. The roadshow. Management presents the business to large investors, who say how many shares they’d like and at what price. Anthropic’s roadshow started on 10 November.
4. The price range. The company publishes the price it expects per share. Anthropic’s range is $70 to $78 for 825 million shares, which adds up to as much as $64.35 billion. The final price can still land above or below the range, depending on demand.
5. Pricing. Shortly before trading begins, the company and its banks fix the final IPO price. Anthropic expects this on 18 November.
6. The first day of trading. The shares start trading on the exchange under a short code called a ticker. Anthropic expects its shares to begin trading on the Nasdaq on 19 November under the ticker ANT.

The first three steps are done. The pricing and first trading dates are the company’s own expectations and could still move.

Key IPO terms explained

• IPO price and opening price. The IPO price is what investors pay if they’re given shares in the offering. The opening price is the first price on the exchange, set by live buying and selling. The two can be far apart, and most investors can only buy at the market price once trading starts.
• Valuation. What the whole company is worth at a given share price. At $78 a share, Anthropic would be valued at about $1 trillion, based on the roughly 13.1 billion shares it’ll have after the deal. Count the extra shares that could be created later, for example from staff share awards, and the figure rises to about $1.4 trillion. That’s known as a fully diluted valuation.
• Float. The part of the company that’s available for the public to trade. Anthropic is offering about 6% of its shares. A small float means fewer shares to go around, which can make price moves sharper in both directions.
• Lockup. An agreement that stops insiders such as founders, staff and early investors from selling for a set time after the IPO, typically 180 days. Anthropic’s is staged. Some staff and directors can sell up to 10% of their locked up shares from the first day of trading, most other restrictions run for up to 180 days, and the founders and larger shareholders are restricted for up to 365 days. When a lockup ends, more shares can reach the market, which can weigh on the price.

What’s confirmed and what’s speculation

A listing of this size produces a lot of headlines, and they don’t all carry the same weight.

Confirmed in the company’s filings and announcements

• Anthropic has filed to list on the Nasdaq under the ticker ANT, offering 825 million shares at an expected $70 to $78 each
• Seven companies that supply its computing power, including Google and Nvidia, have agreed to buy a further $26 billion of shares in a separate private sale at the IPO price

Expected, but not guaranteed

• Pricing on 18 November and the first day of trading on 19 November. Anthropic says the timing depends on regulatory clearance, investor demand and market conditions
• The registration with the SEC hadn’t become effective at the time of writing, and no shares can be sold until it does

Still speculation

• The final IPO price, the opening price and how the shares trade afterwards
• How strong demand is. Reports that the offering is oversubscribed come from unnamed sources, not from the company

The valuation shows the difference. Earlier media reports pointed to as much as $2 trillion. The price range Anthropic filed in November implies about $1.4 trillion at the top, on a fully diluted basis.

How Anthropic compares with other well known IPOs

The size of an IPO is measured by how much money it raises. At the current price range, Anthropic’s offering would raise between $57.75 billion and $64.35 billion. That would make it the second largest IPO on record, behind the $75 billion SpaceX raised in June 2026 and more than double the $25.6 billion Saudi Aramco raised in 2019.

Anthropic’s planned raise next to some of the best known IPOs of the past 15 years, measured by the money raised in the offering itself.

What can happen after the first day

SpaceX is the closest recent comparison, and its first five months on the market show how much a newly listed share can move:

• 12 June: after pricing at $135, the shares closed their first day at $160.95, up 19%
• 16 June: a record close of $201.80, 49% above the IPO price
• 5 August: the lowest close so far, at $108.27, 20% below the IPO price
• 12 November: a close of $139.94, about 4% above the IPO price

SpaceX shares rose almost 50% in their first three trading days, fell below the IPO price within five weeks and have traded on both sides of it since.

The first day has gone very differently across other well known IPOs:

• Alibaba (2014): up 38%
• Arm (2023): up almost 25%
• Facebook (2012): up 0.6%. The shares then fell by more than half in under four months and didn’t close above the IPO price again until August 2013
• Uber (2019): down 7.6%

The risks to keep in mind

• No price history. A new listing has no past trading to refer to, so early price swings can be large
• High expectations. Anthropic reported revenue of $33.2 billion for the first nine months of 2026, up from about $2.5 billion a year earlier. It still made an operating loss of about $1.3 billion over that period and has committed to spending roughly $900 billion over the next two decades, mostly on computing power
• Market mood. New listings often move with their wider sector, and AI stocks have been volatile in recent weeks

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