Will Anthropic claim the biggest IPO market cap in 2026?

SpaceX is currently the biggest IPO of 2026 after going public at a valuation of $1.77 trillion. The stock price closed at $61.11 per share on the first day of trading, giving the company a market capitalization of $2.11 trillion.

At the time, it seemed obvious which company would end the year having posted the biggest market cap on the first day of trading after going public in 2026. Polymarket traders gave SpaceX a chance of about 86% in July, with Anthropic having just 14%.

Fast-forward a little under three months, and a lot has changed. Anthropic is now neck-and-neck with SpaceX to deliver the biggest market cap on the first day of trading in 2026 after confirming its IPO will go ahead this year. Initially scheduled for October, it has been delayed until after the US mid-term elections in November.

Anthropic now has a 47% chance of posting the largest IPO by market cap in 2026 on its debut, just three percentage points behind SpaceX’s 50%.

So can Anthropic’s IPO market cap eclipse SpaceX’s?

First, we need to understand what figure is being talked about when Polymarket says “the largest IPO by market capitalization in 2026.” They are not talking about the market cap based on the IPO price; they are talking about the market cap based on the closing price on the first day of trading.

This means that even though Anthropic’s IPO is forecast to value the company at about $2 trillion versus SpaceX’s $1.77 trillion, there is still the question of how it performs on the first day of trading versus SpaceX.

SpaceX went public at $135 per share. It then rallied 19% on the first day of trading to close at about $161, giving the stock a total market cap of $$2.1 trillion. The stock spiked to hit an intraday peak of $225.64 in the following two sessions, before plummeting below the IPO price six weeks later.

Analysts are predicting Anthropic's IPO could value the company at more than $2 trillion. At such a valuation, the stock would need only a 5% gain on the first day of trading for its market cap to equal SpaceX’s June 12 close. Ideally, this should be an easy target to beat for a company operating in the fastest-growing industry in the market.

Therefore, unless Anthropic significantly lowers its IPO valuation before its debut or underperforms expectations on its first day of trading, it should easily be the biggest IPO of 2026 by market cap, as long as it goes public before the end of the year.