Settlement source

A market asks whether it will be hotter than 85 degrees in New York tomorrow. The reader answers the question in the title. The contract answers a narrower one: what one named document will say about one named place, at one named time. Those usually agree, and the page exists for the days they do not.

How it works

The source is named in the rules, not chosen afterwards. Every exchange and oracle venue in this catalogue writes down, before trading opens, where the deciding figure comes from. The names differ. Kalshi and ForecastEx terms speak of a source agency; the Polymarket US rulebook uses the same phrase for the exchange itself and lists the external sources under it as primary, secondary and tertiary; Polymarket's international markets, Myriad and Futuur put the source inside the rules prose; Limitless names a price oracle by market type. This site calls all of them the settlement source, and the card field markets.resolution_source records it together with who applies it.

On a US exchange the choice is regulated. Core Principle 3 of the Commodity Exchange Act, at 7 U.S.C. 7(d)(3), says the board of trade — the designated contract market — "shall list on the contract market only contracts that are not readily susceptible to manipulation". The Commission's guidance on how to show that, Appendix C to 17 CFR Part 38, says a cash settlement price "should be reliable, acceptable, publicly available, and reported in a timely manner", and that where an independent private third party calculates it, the exchange should consider the need for a licensing agreement and should, where practicable, enter an information-sharing agreement with that provider. That is guidance about what to demonstrate, not a list of approved sources, and the exchange still picks.

Off-chain rules, on-chain readers. On an oracle venue the source is text the oracle is asked to apply. UMA's own description is that each request includes "detailed instructions on how the request should be resolved", which proposers read before proposing an answer. If the named source is ambiguous, the dispute is about the text, and it is settled by a vote — covered under optimistic oracle.

The source is not the authority

Two separate questions hide under "who resolves this market". What does it resolve against — the settlement source. Who reads that source and declares the outcome — the exchange's markets team, a token-holder vote, a question's author. The Kalshi card records both in one line: Kalshi's markets team, as the exchange, against the source named in each market's rules. The Polymarket card records the same kind of named source with a different authority: a bonded proposal to UMA's optimistic oracle. The authority side, with its timetables and appeals, is in who decides the outcome.

Which version of the figure counts

A source publishes more than once. The ForecastEx card records a building-permits contract naming the US Census Bureau and stating that only the initial release counts; later revisions do not change the outcome. A US weather station's daily climate report is itself preliminary, which the temperature guide sets out at length. The settlement source is therefore a document and a moment: the first print, the report at 8:00 AM the next day, the figure as of a stated cutoff.

Why it matters here

The same question on two venues is two contracts. The Polymarket US card records its New York temperature markets settling on the National Weather Service Daily Climate Report for the Central Park station. The Kalshi API card, verified on 19 September 2026, records the settlement source for its NYC temperature series as The Weather Company, which Kalshi took on as its weather source in August 2026. Two identical titles, two documents; on the day those documents disagree by a degree, one venue pays Yes and the other pays No. Anyone pairing markets across venues — for a spread, a hedge or a dashboard — has to pair them on the source, not on the title. The cross-venue matching how-to is built around that.

A source can change under a live series. The Kalshi weather switch above is one case: an archived copy of the same NYC series record from 14 February 2026 lists the NWS Climatological Report as its settlement source, with a note that the NWS Daily Climate Report is the official and final value. The who decides the outcome guide records rules that let an exchange designate a replacement source after trading has started. A source read once, at listing, is the source as of listing.

It is the part of a market a machine can read, on one venue. The Kalshi API card records a settlement_sources list of names and URLs on every series record, readable without an account. Elsewhere in this catalogue the source is a sentence inside rules prose and has to be parsed out. The mechanics of fetching it are in how to read a market's rules from the API; this page only says why it is worth the fetch.

The card field is not the source list. markets.resolution_source on a venue card is one line saying who resolves and against what kind of source. It cannot carry the source for every market, and on a data tool, a client library or a dashboard it is null, because those products settle nothing: the settlement source belongs to the venue whose data they carry.

Being right about the world is not the same as being right about the source. A reader who correctly calls the revised inflation figure, the airport that was hotter than the park, or the league result after an appeal can still hold the losing side, because the contract named a different document or an earlier moment. That gap is where positions that looked correct settle against their holders, and it is visible in the rules before the trade, not only after it.