Kalshi, Polymarket Diverge on Anthropic, OpenAI IPO Odds

Prediction markets Kalshi and Polymarket are offering competing odds on the timing of high-profile 2026 IPOs, including Anthropic and OpenAI, revealing insights into market sentiment and the platforms’ differing event settlement structures. These markets are gaining traction as investors look for real-time signals on companies yet to go public.

SpaceX IPO Sets the Stage

SpaceX’s IPO, which opened on June 12, 2026, serves as a case study for how Kalshi and Polymarket price similar events. By April 1, both platforms were already pricing a 72-74% probability of SpaceX listing by June 30, despite no public filings at the time. Two key developments drove price spikes: a May 15 report detailing an accelerated timeline pushed odds from the high 70s to above 90%, and a May 20 public S-1 confirmed the ticker “SPCX,” lifting odds to 97%.

Both platforms tracked each other closely through to the IPO date. Kalshi hit 99% by June 4, slightly earlier than Polymarket’s 99% on June 6. Despite similar pricing trends, late-stage volume skewed toward Polymarket, which saw $420k in taker-side flow versus just $1k on Kalshi in the final two weeks, as Kalshi’s contracts resolved earlier.

Anthropic Versus OpenAI: Diverging Probabilities

Anthropic is now priced to go public before OpenAI, despite filing its confidential S-1 two weeks later on June 1. On Polymarket, Anthropic’s probability of trading by December 31 sits at 74%, compared to OpenAI’s 53%. Kalshi shows a similar trend, pricing Anthropic’s IPO confirmation at 89% by year-end versus OpenAI’s 64%.

The spread between the two platforms is particularly pronounced for Anthropic’s September 30 cut-off. Kalshi assigns a 60% chance for IPO confirmation, while Polymarket offers just 21% for trading by that date. This 39-point gap highlights uncertainty about Anthropic’s listing timeline but reflects confidence that confirmation will come earlier in the window.

OpenAI Odds Drift Lower

OpenAI has seen its IPO odds decline steadily since early June. Kalshi’s September 30 window dropped from 59% to 24%, while Polymarket’s fell from 39% to 15% in the same period. By December 31, Kalshi prices OpenAI’s IPO confirmation at 64%, with Polymarket giving a 53% chance for trading. The drop aligns with reports of a confidential filing in late May that extended expected timelines.

Market Implications and Liquidity Trends

SpaceX contracts dominated trading volume, with $4.8 million in lifetime notional value now settled. OpenAI’s live contracts have seen $1.24 million in trading, with 70% of activity on Polymarket, while Anthropic has traded $470k to date, split between $271k on Kalshi and $197k on Polymarket. Anthropic’s Polymarket book surged from $12k to $197k in three weeks, reflecting growing interest as its pricing adjusted.

The differences in how Kalshi and Polymarket structure contracts—Kalshi resolving on IPO confirmation and Polymarket on first trade—highlight why spreads persist. These markets also provide unique, independent signals on pre-IPO companies, as pricing reflects third-party sentiment rather than sell-side guidance, offering traders valuable insights into deal timelines.

As prediction markets continue to mature, their divergence in pricing dynamics will remain a critical area for traders to watch, especially with Anthropic and OpenAI now priced for staggered public debuts.

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