Open interest

Open interest is the total notional value of outstanding outcome tokens. On Polymarket this measures how much pUSD value is currently represented by all issued outcome tokens for a market (before settlement).

In plain terms: every outcome token (an ERC-1155 created by the CTF) represents a claim on $1.00 if that outcome resolves. Open interest sums the notional pUSD value of those outstanding tokens across the market, giving a snapshot of how much capital is locked into unresolved positions.

Key takeaways

• Open interest equals the pUSD notional value of outstanding outcome tokens in a market.
• It is reported by the Data API via the /holdings endpoint.
• Open interest is a snapshot of capital committed; it does not equal liquidity or instantaneous tradability.
• Changes in open interest can indicate new position flow, redemptions, or splits/merges.

In context

On Polymarket, outcome tokens are minted and managed by the Conditional Token Framework (CTF). When traders split pUSD into a complete set of outcome tokens, they convert pUSD into outstanding claims; when they merge or redeem after resolution, those tokens are burned and open interest falls. Because each outcome token is notionally worth $1.00 at resolution, summing their counts (weighted by price where applicable) gives the market's open interest in pUSD.

Programmatically, you can retrieve open interest data from the Data API. The Data API exposes positions and holdings; the /holdings endpoint surfaces the outstanding token balances and allows you to compute or read the notional open interest for a given market or condition. For real-time order-book metrics like best bid/ask or midpoint, use the CLOB surfaces instead.

See also

• /glossary/data-api

How this affects your trading

Open interest is a useful indicator of market size and participant commitment. Rising open interest often accompanies new liquidity and interest; falling open interest can mean traders are closing positions or redeeming after resolution. However, open interest alone doesn't tell you about spread, depth, or immediacy of execution — for those you should consult the CLOB order-book endpoints.

When you interpret open interest, remember that it is a notional snapshot. It does not remove resolution risk, slippage risk, or other operational risks associated with trading on Polymarket. Use it as one input among many when assessing a market.