Why Anthropic May Let Early Investors Sell Shares, Unlike SpaceX and Cerebras

Anthropic has confidentially filed for an initial public offering (IPO) and reportedly plans to release its prospectus after Labor Day. The company is considering allowing existing shareholders to sell shares in its IPO. However, it is not clear whether those sellers would be early investors, employees, executives, or a combination of the three.

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Anthropic is also considering lockup periods longer than the customary 180 days for shares that are not sold in the IPO. Hence, the combination could allow some existing shares to enter the public market initially while delaying when a much larger pool of pre-IPO shares becomes available for sale.

Why Anthropic may want more shares available initially

An IPO can include new shares that raise cash for the company, or existing shares sold by shareholders. The latter do not add new shares outstanding.

Space Exploration Technologies, also known as SpaceX, has already demonstrated why this could matter. Only around 5% of its shares were available for public trading after its June IPO. Another 911.5 million shares became eligible to trade after its first lockup expired in August 2026. This has more than doubled its public float (shares available for public trading). Scheduled lockup releases could make as much as 40% of SpaceX's shares potentially tradable by Dec. 8.

Anthropic may take a different approach by allowing some existing shares to be sold in the IPO and locking the remainder for longer. The company is also reportedly considering preset Rule 10b5-1 (prearranged plans that set when and how employees can sell shares) trading plans for rank-and-file employees (employees who are not senior managers or executives). These plans would make future employee sales more predetermined, although they would not themselves restrict how many shares become eligible for trading.

Anthropic also tightly restricts its private shares (shares in a company that is not yet publicly traded), and transfers without board approval are considered void. The company gave employees an option to sell up to $5 billion to $6 billion of shares at a roughly $350 billion valuation earlier this year. However, employees ultimately sold fewer shares than investors wanted to buy. Hence, offering liquidity does not necessarily mean shareholders are rushing for the exits.

Anthropic's IPO structure matters

SpaceX and Cerebras Systems did not have existing shareholders sell shares in their IPOs. Both instead issued new shares, while pre-IPO shareholders could sell later as lockup restrictions were released. Cerebras sold 34.5 million shares itself and raised about $6.2 billion net.

Anthropic has already raised at least $130 billion to support its huge computing needs. The company's IPO could also reportedly exceed the roughly $86 billion raised by SpaceX. However, Anthropic may receive less cash than the headline IPO size suggests, because proceeds from secondary shares go to the shareholders selling them. Hence, the primary-versus-secondary mix will be important. Secondary shares could increase the initial public float, while longer lockups delay when more shares become available for trading.

Employee selling cannot be viewed as inherently negative. Employees may sell for taxes or diversification. Caution becomes warranted if founders or senior executives sell large portions of their holdings, or if secondary shares dominate the offering despite Anthropic's capital needs.

The prospectus should reveal whether Anthropic's IPO is mainly about raising fresh capital or providing liquidity to existing shareholders. It should also show how much stock could become available for sale later.

Manali Pradhan, CFA has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.