In brief
SpaceX is the overwhelming favorite to be the largest IPO by market cap in 2026, with an 85.5% probability on Polymarket. Its $86 billion debut in June 2026 is the largest of the year so far, and no other contender has yet completed a larger IPO. However, its stock has fallen below the IPO price, and short sellers have profited, introducing some uncertainty.
Introduction
The race to become the largest IPO by market capitalization in 2026 is dominated by a single player: SpaceX. The Elon Musk-led company completed a record-breaking $86 billion IPO in June 2026, instantly becoming the frontrunner. While its stock has since declined, no other candidate has yet matched its market cap on the first trading day. This analysis examines the current state of the market, the key contenders, and the factors that could influence the final outcome.
What to know
The Polymarket event resolves to the company that achieves the highest market capitalization on its first trading day in 2026. SpaceX completed its IPO on June 12, 2026, raising $75 billion by selling 555.6 million shares at $135 each, resulting in a market cap of approximately $86 billion [Source 10]. This made it the largest IPO in history, surpassing Saudi Aramco's 2019 listing [Source 13].
Since its debut, SpaceX's stock has fallen. Short sellers have racked up an estimated $8.7 billion in paper profits as the stock slipped below the IPO price [Source 3]. As of July 13, 2026, the stock was down 26% from its post-IPO high [Source 14]. Despite this, its first-day market cap remains the benchmark to beat.
Other potential contenders include xAI, Anthropic, and OpenAI. xAI, also led by Elon Musk, was acquired by SpaceX in Q1 2026 for $250 billion, making it unlikely to have a separate IPO [Source 15]. Anthropic and OpenAI have both filed confidentially to go public, but OpenAI is reportedly considering waiting until 2027 [Source 6]. Polymarket data shows a 75.5% probability that Anthropic will IPO by December 31, 2026, but only a 21.5% chance for OpenAI by the same date [Source 16].
Other notable IPOs in 2026 include Cerebras Systems ($34.3 billion) and SK Hynix's U.S. listing, which was the third-largest of all time [Source 6]. However, none have surpassed SpaceX's market cap. The IPO market is active, with Hong Kong seeing its strongest first half in five years [Source 2], but no new listing has challenged SpaceX's lead.
The market numbers
| Outcome | Implied Probability |
|---|---|
| SpaceX | 85.5% |
| xAI | 25.5% |
| Anthropic | 14.1% |
| OpenAI | 0.8% |
Source: Polymarket, as of July 20, 2026. Total volume: $4,863,613.744. Total liquidity: $907,527.608.
The factors at play
- SpaceX's first-day market cap: At ~$86 billion, this is the largest IPO of 2026 so far. Any competitor must exceed this on their first trading day.
- Post-IPO stock performance: SpaceX's stock has fallen below its IPO price, but this does not affect its first-day market cap, which is already locked in.
- Timing of other IPOs: Anthropic and OpenAI have not yet set firm dates. If they IPO in 2026, their market caps would need to exceed $86 billion to win.
- xAI acquisition: xAI was acquired by SpaceX, making a separate IPO highly unlikely. Its 25.5% probability may reflect market confusion or speculation about a spin-off.
- Market conditions: Geopolitical tensions and tech stock volatility could affect IPO pricing and first-day pops for future listings.
- Regulatory and legal risks: OpenAI faces a trade secrets lawsuit from Apple, which could delay or reduce its IPO valuation [Source 6].
Our prediction
According to our analysis, the most likely outcome is SpaceX. Polymarket currently assigns a probability of 85.5%, while our internal estimate is 90%. The difference stems from these factors: SpaceX has already completed its IPO with a record $86 billion market cap, and no other contender has yet filed for an IPO that would clearly exceed that figure. While Anthropic and OpenAI are potential challengers, their IPOs are not guaranteed to occur in 2026, and even if they do, their valuations would need to be extraordinary to surpass SpaceX. The market may be overestimating the chances of xAI, which has been absorbed by SpaceX.
Risks and uncertainties
- A surprise mega-IPO: A company like Anthropic or OpenAI could complete an IPO with a market cap exceeding $86 billion, especially if AI hype drives valuations higher.
- SpaceX's stock decline: While the first-day market cap is fixed, a significant drop could affect the market's perception, but not the resolution.
- Regulatory delays: Antitrust or securities reviews could delay or alter the terms of potential IPOs.
- Geopolitical events: The Iran war and other tensions could disrupt markets and IPO plans.
- Acquisition or merger: Any contender could be acquired before its IPO, removing it from the race.
Conclusion
Spacex's record-breaking IPO in June 2026 has set a high bar that no other company has yet matched. While the stock has since declined, the first-day market cap is the only metric that matters for this prediction market. Unless a challenger like Anthropic or OpenAI completes an even larger IPO in the remaining months of 2026, SpaceX is on track to win. The Polymarket probabilities reflect this, though we see the gap as even wider.
This content is for informational purposes only and does not constitute financial, political or investment advice, betting advice, or any operational recommendation.