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Arbitrage tracks the same prediction market question across multiple platforms simultaneously. Because “Will BTC reach $100k by 2026?” might trade on Polymarket at 0.62, on Limitless at 0.58, and on Predict.fun at 0.65, you need a single reference point to understand where the market actually stands — and how much the platforms disagree. That reference point is the index.

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Canonical questions

Every market Arbitrage tracks is linked to a canonical question — a single logical event that may be listed under different titles across multiple platforms. When you browse Arbitrage, you are always looking at canonical questions, not raw platform markets. The market_count and platform_slugs fields on each item tell you how many platforms are currently listing that question and which ones.

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Index price

The index_price is a volume-weighted consensus probability on a 0–1 scale, where 0 means the outcome is considered impossible and 1 means it is considered certain. Platforms with higher 24-hour trading volume contribute more weight to the index, so a high-volume venue like Polymarket carries more influence than a low-volume one.
The index price is not a simple average. Volume-weighting means that thin, illiquid markets have less influence on the consensus than deep, actively traded ones.

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Divergence

Divergence measures how far apart the platforms are from each other. Technically, it is the weighted standard deviation of Yes prices across platforms. A low divergence means the platforms broadly agree; a high divergence means there is significant disagreement — and potentially an opportunity worth investigating. Arbitrage groups divergence into three categories:

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The DiscoverItem schema

Every item returned by the discovery endpoint includes these fields:

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The IndexResult schema

When you fetch a specific question via GET /api/v1/questions/{id}, the response includes a detailed index object:
The platform_prices map gives you the individual Yes price for each platform, so you can see at a glance exactly where the disagreement lies and which venues are on either end of the spread.