Neg-risk

A question with one winner out of many — an election, a championship, a central-bank decision with five possible moves — looks on Polymarket like one market with a list of outcomes. Underneath it is a stack of separate binary markets, one per outcome, each with its own YES token, NO token and order book. Neg-risk is the name for the machinery that makes the stack behave like one market, and the flag every tool reading Polymarket data has to check before it adds, signs or redeems anything.

How it works

The equivalence it exploits. Polymarket's adapter README gives the canonical example: an election with candidates A, B and C, one binary market each. A position of one NO on A and one NO on B is worth 1 USDC if A wins, 1 if B wins and 2 if C wins — exactly the same as 1 USDC plus one YES on C. Because only one outcome can win, those two positions are interchangeable, and the NegRiskAdapter contract performs the swap.

The conversion. In the adapter's own notes: if a market has n questions and you convert an amount of m NO tokens, you receive that amount times m − 1 in collateral, plus the same amount of YES in each of the outcomes you did not hold NO on. The NO tokens are burned. Polymarket's concept page states the one-outcome case as "a No share in any market can be converted into 1 Yes share in every other market". The adapter has an optional fee rate on conversion, paid to a vault contract; whether a given market charges it is a market parameter, not a constant.

Why the prices sum to about one. Exactly one YES in the group pays a dollar, so a full set of YES tokens is worth exactly a dollar at settlement. If the best asks across every outcome add up to less than that, buying one of each locks in the difference before fees. If the bids add up to more, buying a NO on every outcome and converting all of them returns n − 1 dollars immediately rather than at resolution. The conversion is what makes the second trade release cash now, and the two together are what hold the sum close to one. Close is not equal: reading the 40 open Polymarket events with the most 24-hour volume on 4 October 2026, nine were flagged negRisk, and their YES outcomePrices summed to between 0.92 and 1.07. Spreads, thin books on long-shot outcomes and fees all sit in that gap.

Augmented neg-risk. Plain neg-risk needs every outcome known at creation. The augmented form adds named outcomes, unnamed placeholder outcomes that can be assigned later — a candidate who enters the race — and an explicit "Other". Polymarket's documentation says to trade only named outcomes, that its interface hides unnamed ones, and that "Other" changes meaning each time a placeholder is clarified. The adapter README says why "Other" has to exist: a neg-risk group in which every question resolves NO, or two resolve YES, cannot be resolved cleanly.

Why it matters here

It is a field you have to read, not a detail you can ignore. Gamma returns negRisk, negRiskMarketID and negRiskRequestID on each market, and enableNegRisk and negRiskAugmented on the event; the CLOB returns neg_risk on the order book and answers a dedicated GET /neg-risk lookup by token ID. Membership is a market-level property, augmentation an event-level one, so a tool needs both reads to know whether to show placeholders. The Gamma API and CLOB API cards cover the endpoints.

Orders go to a different contract. Polymarket's order-placement guide uses the book's neg_risk value to choose the exchange contract that is the order's EIP-712 verifying contract: one address for standard markets, another — the Neg Risk CTF Exchange — for neg-risk ones. Splits, merges and redemptions likewise go to a separate neg-risk collateral adapter. A client that hard-codes the standard path produces signatures and calls aimed at the wrong contract. This is why the Polymarket CLI has a separate ctf redeem-neg-risk, and why the Limitless SDK card notes that Limitless's NegRisk groups take a different order path from its plain markets.

Profit and loss needs a correction. A conversion moves value with no counterparty and no trade: NO tokens disappear, YES tokens and cash appear. A wallet tracker that reads only fills sees a position vanish at no price. OrcaLayer labels its win rates NegRisk-corrected for this reason, and PolyTaxes lists neg-risk conversions as their own transaction type in its cost-basis matching. The volume guide explains why conversions are kept out of turnover by the people who measure it carefully.

Summing an event is not a sanity check you can skip. A dashboard that adds every market Gamma returns for an augmented event includes placeholders and an "Other" whose definition has drifted. The total will not be one, and nothing is wrong with the venue.

The name says nothing about risk. "Negative risk" describes the capital efficiency of the conversion — a position against one outcome is the same as a position on all the others — not a position that cannot lose. Every leg of a neg-risk group is still an ordinary conditional token that pays zero if it is wrong.