Polymarket vs PredictIt

PredictIt caps position sizes at a few hundred dollars per market, charges fees on realized returns, and requires U.S. registration tied to its CFTC no-action relief. Polymarket is a global order book with no per-user position cap, trades indexed to USDC, and settles off a reference price — the exact mechanics archived at 250ms on this site.

Neither is a substitute for the other: PredictIt is the right answer for small, compliant, research-graded forecasts, while Polymarket is the right answer for anyone who wants real depth, real speed, and an audit trail of what the book did second by second.

The single most instructive difference is data cadence. PredictIt prices move on human auction cadence and its historical quotes are coarse; Polymarket order books are captured four times per second, so an event like a Chainlink reference print reprises the ladder inside the same second the underlying moved.

That measured fact matters for anyone building on this data: a 250ms book can show the 0.065-to-0.815 collapse the same second Binance printed its low, and no coarse feed can reproduce that window. The settlement-minute studies on this site are only possible because the books were stored whole.

PredictIt charges a 10% fee on profit per market (capped) and an additional 5% on withdrawals, plus the position caps. Polymarket has no trading fee and no counterparty margin call; the cost of trading is mostly slippage against a thin one-sided book, which is measurable: 5-minute markets are one-sided 16.9% of the time and 3.24% of snapshots are crossed.

What you trade on Polymarket is a small tick grid — executable prices sit on the 0.5-cent and 1-cent grid 98.6% of the time — so the real cost is the spread, and the honest way to measure it is from the stored books rather than a fee table.

PredictIt offers a public API with coarse market data and no full-L2 historical archive behind it. Polymarket's official API serves live books and 1-minute price history, and recorded 250ms depth is what the archive on this site provides — every bid and ask level with sizes, plus prices and metrics on the same grid.

The research consequence is direct: any backtest of a PredictIt strategy has to work from quotes, while a Polymarket backtest can replay fills off the actual ladder. That is the difference between modeling a price and modeling a market.

Choose PredictIt when you need a compliant, small-stake, U.S.-facing research venue and the coarse cadence is fine for the question. Choose Polymarket for real depth, sub-second cadence, and an archive you can cite. For traders the two are not really alternatives; they are different instruments.

For data work specifically: if you need yesterday's book at a recorded second, there is only one of the two venues that can produce the frame, and the frame lives in a 250ms archive.

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