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Self-trade prevention (STP) stops your orders from filling against your own resting orders. It runs on the matching engine for every order, it is not an order parameter, and it cannot be disabled or changed per order.

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How it works

Before a taker matches, the engine checks whether the resting maker it would hit belongs to the same party. Every order submitted through the API runs in CancelMaker mode: the conflicting resting order is canceled and the taker keeps matching against the rest of the book. The canceled resting order is reported with status stp_cancelled, the same status you see in the order tables under Trading. The engine also implements CancelTaker and CancelBoth modes, which are used internally by the exchange and are not available to API orders. STP acts on resting orders that are eligible to match. A resting order priced outside the instrument’s mark-relative price band cannot be matched by anyone, so a crossing order of yours does not cancel it; it stays on the book, keeps its margin reserved, and counts toward your open-order limit until you cancel it or the mark moves back into range.

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Account groups

Polymarket can group several accounts that are controlled by one entity, for example a market maker running separate accounts for separate strategies. Groups are assigned by Polymarket on request. There is no public API to create, inspect, or change them, and group membership is never visible to other users or in public endpoints. For STP, accounts in a group count as the same party. An order from one member that would match another member’s resting order cancels that resting order and continues matching against the rest of the book, exactly as if both orders were on one account. Resting take-profit and stop-loss exits behave like any other resting order of yours: a group-mate’s crossing order cancels them just as your own would, and a canceled exit does not re-arm. Grouping changes nothing else about how the accounts trade. Balances, margin, positions, liquidation, rate limits, open-order limits and auto-cancel remain strictly per account. Two things do follow group membership besides STP:
  • Default leverage and margin mode. A group can carry defaults that apply to any member with no explicit per-instrument setting, including future listings. Your own explicit settings always take precedence. See Margin.
  • Internal transfers between members. When Polymarket enables the feature, a trading key registered to one member can move collateral to another member of the same group. Owner keys are never restricted by groups, and withdrawals always require the owner key.
When Polymarket changes a group’s membership, orders that were being matched at that instant are re-evaluated by the engine against the new membership before any result is published, so a fill or cancellation can never be based on stale membership. You do not see a distinct error for this; the order simply resolves under the new membership. To have accounts grouped, contact Polymarket with the list of accounts that belong to the entity.