Prediction Market Comparisons.
Live data, methodology, every venue.

Depends on what you need. For CFTC-regulated USD-denominated trading on US-political contracts, Kalshi. For maximum global liquidity on flagship contracts (geopolitical, crypto, sports), Polymarket. For long-horizon panel forecasts, Metaculus. For play-money community forecasting at scale, Manifold. For an AI-driven on-chain protocol with the OPN token ecosystem, Opinion. The /compare/kalshi-vs-polymarket page surfaces live volume, spread, and matched-market gaps so you can pick by depth instead of brand.

A prediction market lets traders buy and sell binary contracts that pay out based on a real-world outcome — the live price is a probability estimate weighted by stake. A poll asks a sample of people what they think, which measures opinion at a moment in time but does not aggregate stake-weighted information the way a market does. Markets update continuously; polls are episodic. See /compare/prediction-markets-vs-polls for historical accuracy across the 2008-2024 election cycles.

Both list overlapping U.S. political contracts. Kalshi is a CFTC-regulated U.S. exchange (USD, KYC) while Polymarket is a crypto-settled platform (USDC, on-chain). Kalshi tends to have deeper U.S.-resident retail participation; Polymarket tends to have higher absolute volume on flagship contracts. /compare/kalshi-vs-polymarket shows live volume, spread, and matched-market gaps so you can pick by current market depth.

Different liquidity pools, different participant mixes, and different fee/settlement mechanics produce real cross-venue spreads. We surface those as cross-venue gaps on /compare/kalshi-vs-polymarket and on the live screener at /screen — they are tradeable signals, not data errors. The cross-venue arb pair table at /api/public/cross-venue/pairs?preset=arb returns matched contracts with current spreads.

Prediction markets and Metaculus both produce calibrated probability estimates; markets typically lead on liquid, near-term, financially settled questions while Metaculus tends to lead on long-horizon and esoteric forecasts where money does not flow. Polls are accurate for opinion measurement but are not designed to forecast — they are a single snapshot. We publish per-venue Brier scores at /api/calibration so you can audit live: currently Kalshi 0.20, Polymarket 0.12 on T-24h price over the past 90 days.

For AI agents and autonomous trading systems that need normalized cross-venue data plus thesis system plus calibration plus CLI/API-first agent surfaces, SimpleFunctions ships the deepest agent-callable surface. For institutional Kalshi order routing with FIX 4.4, the native Kalshi REST + FIX is the right answer. For Polymarket-only on-chain trading, the Polymarket CLOB v2 is canonical. For maximum venue breadth across PredictIt + ProphetX + Opinion in addition to Kalshi + Polymarket, Prediction Hunt v2 covers the most ground. See /compare/prediction-market-apis for the full 11-API comparison.

Yes — 9 MCP servers covering Kalshi, Polymarket, and related venues. SimpleFunctions ships the largest first-party MCP catalog in this comparison, spanning normalized cross-venue reads, screener over computed indicators, calibration scores, causal-tree thesis system, and authenticated intent execution. Several open-source servers exist for individual venues (JamesANZ, guangxiangdebizi/PolyMarket-MCP, berlinbra/polymarket-mcp). Full comparison at /compare/prediction-market-mcp-servers.

Live data fields (volume, market counts, calibration) are pulled directly from the SimpleFunctions API on each request. Methodology fields (regulation, settlement currency, fee structure) are verified manually from public sources at the date stamped on each comparison. Every page links the underlying live endpoint so you can reproduce the numbers with curl.