Kalshi and Polymarket both run "IPO by date" markets on all three names, and they settle on different events. Kalshi resolves when the company confirms an IPO: the SEC declares the S-1 effective, the deal prices, or an exchange assigns a ticker. Polymarket resolves when shares actually open for trading. In a normal IPO these two events are one to two business days apart, so the two venues should track closely. Where they pull apart, it reflects the two crowds pricing the same dated question differently, often because the cutoff falls near the expected listing. The dates align cleanly: Kalshi's "before the 1st of a month" is the same cutoff as Polymarket's "by the last day of the month before."
SpaceX listed in mid-June and both venues' June contracts have stopped trading, so this is the one outcome we can grade.
By April 1 both venues already priced a SpaceX IPO by June 30 at about 72 to 74 percent, ahead of any public filing, and the confidential S-1 that day moved nothing.
Two later events did the work, and both venues reacted on the same day each time:
They crossed 90 percent on the same day and held within a point or two of each other all the way up, then resolved together when shares opened on June 12. Kalshi reached 99 percent on June 4, two days before Polymarket on June 6, a small gap that closed at the listing.
Late volume rotated to the venue still pricing an open question: over the market's life Kalshi traded more, $2.66M against $2.17M taker-side, but in the final two weeks nearly all flow was on Polymarket, about $420k against roughly $1k, as the announcement settled and only the listing remained live.
OpenAI has repriced lower across every window since early June. Its chance of an IPO by September 30 fell from about 59 percent (Kalshi) and 39 percent (Polymarket) on June 2 to 24 and 15 percent now.
The December 31 window dropped from 86/71 to 64/53
Both venues now put a 2026 listing below even odds for most of the year and only modestly likely by December, and the two sit close together, so they broadly agree on the timing. The move lines up with the May 20 reports of a confidential filing around May 22, after which the timing odds drifted out rather than in.
Anthropic prices ahead of OpenAI on a like-for-like basis. Comparing the two on Polymarket alone, where both are measured by first trade, Anthropic is higher at every cutoff: 21 percent versus 15 percent by September 30, and 74 versus 53 by December 31. The market sees Anthropic reaching public trading sooner, despite filing its confidential S-1 two weeks later, on June 1.
Anthropic also shows the widest split between its two venues of any name here. Kalshi puts a 60 percent chance it confirms an IPO by September 30; Polymarket puts a 21 percent chance it is trading by then. Since confirmation and trading are normally days apart, that 39-point gap is not a long lag. It reflects uncertainty about whether the listing lands before or after September 30, concentrated at that one cutoff, with confirmation expected on the early side of it.
The gap narrows to 15 points by December 31, at 89 and 74, as both events move inside the window.
Lifetime taker-side notional:
Anthropic's Polymarket book grew from $12k to $197k in three weeks, and its price correction tracked that growth. SpaceX traded almost $5M over its life but went quiet the moment it listed. Anthropic's Polymarket book filled in only after it filed, and now leads Kalshi on recent flow.
Methodology notes: Figures as of June 24, 2026. The two contracts settle on events usually one to two business days apart, so a spread between venues measures disagreement at a given date, not a filing-to-listing lag. Each venue's curve gives a median date only for its own event. The two venues have separate users with no arbitrage between them, so a spread can persist.
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