Glossary
Open interest
The stock of live outcome tokens that have not been merged or redeemed. Volume is flow; open interest is inventory still in the event.
Open interest on Polymarket is the stock of live conditional tokens — how many YES/NO shares (or NegRisk YES legs) exist because someone split collateral and has not merged or redeemed yet. Volume is the flow: how many shares changed hands today. A market can print huge volume on a revolving short-term contract while OI stays modest; a neglected election book can sit with large OI and almost no tape.
OI goes up when traders split $1 of USDC into a complete YES/NO set (or the NegRisk equivalent) and goes down when they merge sets back or redeem after resolution. Buying YES from a maker who already holds it does not create OI; it just changes who owns the inventory.
Do not treat OI as “how much money will be paid out.” At most one dollar per complete set is at risk, and many tokens expire worthless. It is a better proxy for how much inventory is stuck in the event than for tomorrow’s volume. Polydata market pages emphasize volume and traders because that is what our warmed feeds carry cleanly. When we talk about crowded books, we mean tape and holders — not a futures-style OI copied from a CME glossary.