Via gemini.com
The crypto exchange's new sealed-bid auction system for multi-leg prediction contracts enters sandbox testing as competition heats up with Kalshi and Polymarket
Gemini is rolling out a new trading tool that brings Wall Street-style execution mechanics to prediction markets. The exchange’s Custom Combos feature, now live for beta testing in its sandbox environment, lets market makers submit sealed bids on multi-leg prediction market contracts through a Request-for-Quote API.
How the system actually works #
The RFQ process runs on a tight clock. Market makers get a 1-second window to submit their quotes after a request comes in. The requester then has 5 seconds to accept the best bid. Finally, the winning maker gets a 1-second “last-look” confirmation period to finalize the trade.
That entire lifecycle runs through a series of defined states: OPEN, PENDING_ACCEPTANCE, CONFIRMING, and FINALIZING. The whole thing wraps up in roughly 7 seconds.
The sealed-bid design means competing market makers can’t see each other’s quotes. Only the winning bid gets disclosed after the auction concludes.
Contracts require at least two legs, which means traders can construct custom combinations of prediction market positions rather than being limited to single-outcome bets.
Production access remains locked down during this controlled beta phase. Developers and market makers can only integrate and test through the sandbox environment. Gemini’s documentation for the feature was last updated on August 11, 2026, laying out the full operational flow, messaging formats, and timing specifications.
The prediction markets arms race #
Gemini entered the prediction markets space in late 2025, and Custom Combos represent its bid to differentiate in an increasingly crowded field. Kalshi and Polymarket both rolled out similar combo capabilities earlier in 2026.
Where Gemini’s approach diverges is in the execution model. Rather than matching orders on a central limit order book, the RFQ system creates a private marketplace where institutional liquidity providers compete for flow.
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