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Parameters

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market_id
string
required
Native market identifier. Kalshi: ticker. Polymarket: condition ID.

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Returns

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open_interest
f64
Total outstanding contracts across both sides of the market.
Kalshi reads open_interest_fp from the market summary endpoint. Polymarket uses Data API GET /oi?market={condition_id} and returns an explicit error when the Data-API miss has no value, rather than silently returning 0.
let oi = ex.fetch_open_interest("KXBTC-25MAR14-T20000").await?;

4280.0