Anthropic's IPO Is Coming. Here's What That Means for S&P 500 Investors.

Anthropic's planned IPO, anticipated no earlier than mid-October, is anticipated to gauge the appetite of financial markets for AI-related investments. The S&P 500's performance will hinge on the IPO's outcome. The company is targeting a valuation surpassing $2 trillion, potentially making it the largest IPO in history, surpassing Space Exploration Technologies.

Investors should not anticipate immediate S&P 500 funds purchasing Anthropic, as the integration process will be gradual and potentially disruptive. The journey to the S&P 500 is expected to be a slow one, potentially causing some investors to feel unease. Most investors perceive they missed the AI wave by not investing in Nvidia in 2005, but according to analysts, they are merely at the conclusion of the research and development phase.

Act 2, encompassing global deployment, is yet to begin. Currently, S&P 500 index funds must comply with specific criteria for inclusion, which Anthropic may not meet due to its recent public listing and lack of positive earnings under generally accepted accounting principles (GAAP). Although SpaceX joined the Nasdaq-100 within weeks of its June 2026 IPO, it is yet to be included in the S&P 500.

If Anthropic follows the same timeline, its earliest opportunity to join the S&P 500 may be in late 2027. Despite this, two of the index's largest constituents already hold Anthropic, suggesting existing exposure. For example, Amazon generated $16.8 billion in pretax earnings from its Anthropic stake in Q1 2026, while Alphabet also holds a stake in the company.

Historically, on average, U.S. IPOs have experienced a 19% gain on the first day, but long-term performance often underperforms the market by 25.5% over three years. AI stocks accounted for over 80% of the S&P 500's gains through mid-May 2026. Consequently, a lukewarm response to Anthropic's IPO could suggest a waning interest in AI, adversely affecting AI-heavy index funds.

While Anthropic's IPO could prove beneficial for long-term investors and index funds upon inclusion, in the short term, it poses a risk to the S&P 500, representing the potential downsides of early AI investment.