Anthropic's IPO Will Follow SpaceX's Playbook of Fast Index Entry and Forced Buying

The company aims to raise up to $64.4 billion by selling 825 million shares at $70 to $78 each, a range that would value it at up to $1.4 trillion. It is also raising $26 billion in a separate private sale to cornerstone investors including Alphabet's Google, Nvidia and Advanced Micro Devices. Those shares carry no lock-up.

The size of the deal is what makes the new rules matter. Intropic, a London-based firm that analyses index rebalances, estimates that index-tracking funds will need about 28% of the shares on offer, or roughly $19 billion. Only about 6% of Anthropic's outstanding shares are being sold in the IPO, so that guaranteed demand meets a small float. Hedge funds and index-rebalancing funds are expected to bid for shares early so they can sell to the passive funds later.

Carsten Hesse, London-based head of index events at Berenberg, called Anthropic "a mirror image of the SpaceX IPO" with "the same index-related drivers over the first 15 days of trading."

What Happened With SpaceX

SpaceX's $75 billion offering valued the company at nearly $1.75 trillion. It set aside a fifth of the shares for retail investors, more than double the usual allocation, and Anthropic is doing the same. Index funds and retail buyers took nearly half of the SpaceX shares sold, and other fund managers bought ahead of that demand.

SpaceX sold its shares at $135 and opened at $150. By the third day of trading the stock was 50% above that opening price, and it stayed well above the IPO price for the first 15 days. It then drifted lower as investors prepared for the first lock-up expiries, when employees and other pre-IPO holders could start selling. SpaceX and SK Hynix, which listed on Nasdaq in July, both jumped on their third day of trading. That was when options on the shares became available and dealers selling those options bought stock to hedge. Analysts expect the same early buying in Anthropic.

"As we've seen with SpaceX, people are buying early," Hesse said. Ruben Pathmanathan, an equity analyst at Intropic, said index inclusion, passive demand and a tightly held float together shaped how SpaceX was priced and traded in its first days.

Where Anthropic Differs

Anthropic will let employees, who own roughly 15% of its equity, sell some shares on the first day of trading. That adds supply SpaceX did not have, and the cornerstone shares without a lock-up could add more.

For arbitrage funds, deals this large are welcome. Index trades have usually been limited by the size of the IPO, with too many funds chasing too little passive demand. "This is the type of opportunity that the arbitrage community likes because the risk of overcrowding is more limited," said Celia Fseil, head of equity market neutral strategy at Candriam. Brian Hartigan, global head of ETFs and index investments at Invesco, described it as "a bit of an evolution of the market."

The sums can be large. Bloomberg reported that two teams trading index changes at Millennium Management made $3.7 billion in June. Millennium would not confirm the report. Bill Park, chief investment officer of Connecticut-based Altisma Capital Management, said that for index rebalancing traders, "these are probably the events of a lifetime."

The first test is pricing and the opening trade next week. After that, the index additions fall within 5 to 15 days, and options trading, which moved SpaceX on its third day, will be watched closely.