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Cross-Platform Spread

Pull the YES price for the same real-world question from every venue that lists it, in one API call.

Note

This recipe replaces the old "build your own correlation index" approach in cross-platform arbitrage. Recent versions ships the correlation built-in — no manual matching required.

Walkthrough

Find a multi-provider event
```
bashTOKEN="art_live_..."
 
curl 'https://api.artery.questflow.ai/v1/events?underlying=BTC&min_providers=2&limit=5' \
  -H "Authorization: Bearer $TOKEN"
```
min_providers=2 filters to events where ≥2 providers list the same canonical question. Without it, you also see single-provider events.

Fetch the live spread

bashEVENT_ID=evt_94c9a200-8152-43b1-8b10-46214bea101a
 
curl "https://api.artery.questflow.ai/v1/events/$EVENT_ID/spread" \
  -H "Authorization: Bearer $TOKEN"

Response:

json{
  "universalId": "evt_94c9a200-...",
  "fetchedAt": "2026-05-09T04:01:30.123Z",
  "legs": [
    {
      "provider": "polymarket",
      "providerMarketId": "0xa8aceb...",
      "yesBid": 0.999,
      "yesAsk": 1.0,
      "yesMid": 0.9995
    },
    {
      "provider": "kalshi",
      "providerMarketId": "KXBTCD-26MAY0917-T69999.99",
      "yesBid": 0.99,
      "yesAsk": null,
      "noBid": null,
      "noAsk": 0.01,
      "yesMid": null
    }
  ]
}

YES prices are normalised to dollars (0–1). Each leg's yesBid / yesAsk / yesMid is computed from that provider's native orderbook in parallel; one leg failing doesn't block the others.

Detect edges

tstype Leg = { provider: string; yesBid?: number; yesAsk?: number; yesMid?: number };
function detectEdge(legs: Leg[]) {
  const valid = legs.filter((l) => l.yesMid !== undefined);
  if (valid.length < 2) return null;
  const sorted = [...valid].sort((a, b) => a.yesMid! - b.yesMid!);
  const cheapest = sorted[0];
  const richest = sorted[sorted.length - 1];
  const grossEdge = richest.yesMid! - cheapest.yesMid!;
  // Subtract conservative round-trip fees (0.3% Polymarket, 0.7% Kalshi
  // per side — figures in /providers/* docs).
  const netEdge = grossEdge - 0.01;
  return netEdge > 0
    ? { buy: cheapest.provider, sell: richest.provider, netEdge }
    : null;
}

Subscribe to live mids
Recent versions add artery:stream:event:<universalId> channels that push spread snapshots every time any leg's mid moves. Until then, poll /v1/events/:id/spread at the cadence your strategy needs (typically 1-5 Hz for daily-resolution price binaries).

Per-provider price semantics

Provider	What `yesAsk` represents
Polymarket	CLOB best SELL-side price for the YES token, in dollars (Polymarket quotes 0–1 directly)
Kalshi	Implied: `1 - best NO bid` (from `orderbook_fp.no_dollars`). Direct YES ask isn't quoted by Kalshi — only YES bid is
Hyperliquid HIP-4	`levels[1][0].px` from `info/l2-book?coin=<asset_id>` — best ask in dollars

Warning

Settlement risk — Polymarket settles via UMA Optimistic Oracle, Kalshi via CFTC-regulated DCM rules, HL HIP-4 via on-chain price oracle. The same canonical event can settle differently across venues if the underlying data sources diverge near the strike. A future release will add a settlement_consensus_score per universal event.

Why prices may not align

Even when canonical match is exact, observed mids can differ for legitimate reasons — these are not Artery bugs:

Reason	Example
Different settlement times	Polymarket "by May 9" = midnight ET; Kalshi `26MAY0917` = 17:00 ET; the implied ≥-strike probability differs slightly because there are extra hours of price action
Liquidity-driven spread	Polymarket's BTC-binary book is deeper than Kalshi's by ~10x; Kalshi quotes wider
Settlement-source risk pricing	UMA disputes have settled some Polymarket markets opposite the consensus; arbitrageurs bake that risk into the price
Stale book on one side	One leg may have last traded minutes ago while the other is fresh

Real arbitrage opportunities are typically the small, persistent gaps after fees. Use the snapshot data to make decisions; route execution through official SDKs — Artery does not wrap trade endpoints today (trade endpoints are on the roadmap).

Cross-Platform Spread#

Walkthrough#

Per-provider price semantics#

Why prices may not align#

See also#

Cross-Platform Spread

Walkthrough

Per-provider price semantics

Why prices may not align

See also