From SpaceX to Anthropic, the market has new strategies for dealing with tech giants' IPOs

Mega-IPOs are giving rise to new market trading dynamics: passive funds resulting from index inclusion may become a key force driving the stock price of major companies during their early days of listing.

According to a recent Reuters report, Anthropic plans to issue 825 million shares at a price of $70 to $78 per share, aiming to raise up to $64.4 billion, which would give it a valuation as high as $1.4 trillion. Similar to SpaceX's IPO in June this year, Anthropic is expected to be included in at least six major indices—such as the FTSE USA Index, the S&P Total Market Index, and the Nasdaq 100—within five to fifteen trading days after its listing, thereby triggering concentrated buying from passive funds.

This arrangement means that the share price movement of Anthropic in its early listing phase may not be entirely determined by organic market demand, but instead be significantly influenced by expectations of index inclusion and passive capital inflows. Investors may position themselves ahead of formal index inclusion, further amplifying initial buying pressure.

Index rebalancing analysis firm Intropic estimates that the demand from passive funds tracking related indices for Anthropic shares may amount to 28% of this issuance, equivalent to about $19 billion. The SpaceX IPO has already demonstrated this pattern, and now Anthropic is set to become another example, creating new opportunities for index arbitrage traders as well.

Index Rule Changes, Passive Capital Moves in Early

This shift stems from changes in component stock inclusion rules by major US index providers such as the Nasdaq.

Previously, large companies typically had to wait weeks or even months after listing to be included in major benchmark indices. The new rules, however, allow qualifying mega-IPOs to complete index inclusion within 15 days after listing, enabling pent-up passive fund demand to be released at the early listing stage.

Carsten Hesse, Head of Index Events at Berenberg in London, stated that Anthropic will mirror the SpaceX IPO, facing similar index-driven factors within 15 days after listing.

Intropic equity analyst Ruben Pathmanathan noted that index inclusion, passive fund demand, and highly concentrated float collectively influenced the initial pricing and trading trajectory of SpaceX in its debut phase.

Because passive funds need to allocate shares after the inclusion, active investors may buy in advance to capture price advantages before passive capital enters.

SpaceX Share Price Surged 50% in Three Days After Listing

SpaceX's IPO experience provides a real-world reference for this pattern.

SpaceX opened at $150 per share, and by the third trading day, the stock price had climbed 50% above the opening price, continuing to trade above the $135 IPO offering price within 15 days after the IPO.

The third trading day was precisely when stock options trading commenced. Derivatives traders bought the underlying shares to hedge related positions, further adding to buying pressure. Analysts anticipate that similar advance positioning and hedging might occur during Anthropic's listing as well.

Hesse said market participants won’t wait until Day 5, 10, or 15 post-listing but will instead position around index inclusion expectations ahead of time.

The issuance structure also played a role. About one-fifth of SpaceX's $75 billion offering was allotted to retail investors, and Anthropic adopted a similar arrangement. During the SpaceX IPO, index funds and retail investors together absorbed nearly half of the shares issued, and other fund managers positioned in advance, further magnifying the supply-demand imbalance in the initial free float.

Anthropic’s Points of Difference

Although the two companies share similar IPO paths, Anthropic’s share supply arrangements are distinct.

This IPO involves only about 6% of Anthropic’s equity, so the initial float is relatively limited. However, employees holding roughly 15% of the shares are permitted to sell a portion on day one of listing, which may increase early supply and put some pressure on the stock price.

Additionally, Anthropic is raising $26 billion from cornerstone investors through an independent private placement, with participants including Google (under Alphabet), Nvidia, and AMD. These shares are not subject to a lock-up period, adding further variables to the potential free float after listing.

Therefore, while passive capital’s potential demand is considerable, the ultimate share price performance will still depend on whether buying power can absorb the new supply.

Index Arbitrage Sees Rare Opportunity

The combination of mega-IPOs and new rules for rapid index inclusion also creates rare opportunities for funds specializing in index constituent adjustments.

Brian Hartigan, Global Head of ETF and Index Investments at Invesco, described this phenomenon as a market evolution, attributing it to the massive size of private equity accumulated by mega-companies prior to listing.

Celia Fseil, Head of Equity Market Neutral Strategies at Candriam, noted that such opportunities are favored by arbitrage traders due to relatively limited overcrowding risk. Traditional index rebalancing trades are often constrained by IPO size, meaning passive fund demand is limited and aggressive active pre-positioning can crowd trades; mega-IPOs significantly expand the size of potential passive buying, giving arbitrage strategies much more room to operate.

According to Bloomberg, Millennium Management's two teams that focus on index event-driven trades generated $3.7 billion in profits in June alone this year.

Bill Park, Chief Investment Officer at Altisma Capital Management in Connecticut, said that for investors engaged in index rebalancing trades, such events could be among the most important trading opportunities of their lifetime.