No free source is both tick-fresh and historically complete: a research stack must join at least three surfaces

Asked:

“What public data sources exist for prediction market analysis: Polymarket API, Kalshi API, on-chain data, and how fresh and complete is the data?”

Eight documented data surfaces across Polymarket, Kalshi, Polygon on-chain logs and Dune, compared as of 9 October 2026 from three independent documentation hosts (one URL per surface). Each is placed by how fresh its data arrives and how much history it retains; the top-right quadrant — realtime and permanent — is empty.

realtime stream on-demand / current snapshot minutes after finality hourly refresh historical archive / cutoff tier ◇ outline = free API key required · * paid for most curated tables

Polymarket fine price history is rolling, not permanent: raw/one-minute lasts at least 7 days, five-minute 60 days, thirty-minute 90 days; only twelve-hour (and three-hour from July 2026) series are kept forever — docs.polymarket.com

Current CLOB books are hashed snapshots with no depth archive, so tick-by-tick depth exists only if you record the stream yourself — docs.polymarket.com

Kalshi partitions data at per-datatype cutoffs that advance over time: a complete trade, fill or candlestick history requires merging live and historical endpoints — docs.kalshi.com

Polygon ERC-1155 logs are auditable and complete only when indexed from deployment blocks — and they never contain unfilled or canceled off-chain orders — docs.polymarket.com

Dune lands raw Polygon data within minutes of finality and curates hourly, but most curated prediction-market tables are gated behind a paid entitlement — docs.dune.com

Recommended stack by use case

Live trading and microstructure

Kalshi orderbook WebSocket (snapshot then deltas) and Kalshi orderbook REST for depth checks; Polymarket CLOB books polled with hash-change detection, plus PolyBolt for reference-asset prices. Archive the streams yourself — no venue keeps tick-level depth.

Historical forecasting and backtests

Polymarket Data API v2 for trades, resolutions, open interest and permanent coarse price history; map tokens via the Gamma discovery API first. Kalshi live + historical endpoints merged across the cutoff. Pull fine grains before their rolling windows expire.

Audit and settlement research

Polygon ERC-1155 logs indexed from deployment blocks for fills, transfers, resolutions, redemptions and migrations; Dune raw/decoded tables as a faster query layer. On-chain data cannot reconstruct resting or canceled off-chain orders.

All eight surfaces

Surface	Operator	Access	Freshness	Completeness caveat	Source

Comparison of 8 documented prediction-market data surfaces (one row per source URL) across 3 independent documentation hosts — docs.polymarket.com, docs.kalshi.com, docs.dune.com — reviewed as of 2026-10-09. Chart positions are editorial readings of each page's stated freshness and retention; long access, coverage and caveat text is truncated in the table for space (full detail at each linked page). Gamma API (gamma-api.polymarket.com) and the Bridge API are referenced as discovery/ancillary surfaces on the rate-limits page but are not separate rows.

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