Contract terms · read 27 and 31 October 2026
Midterms 2026: what “control” of the Senate and House means on each venue
Kalshi, Polymarket International and Polymarket US all list which party will win the Senate and House on 3 November 2026. Their contracts use different definitions, sources, deciders and timing. A side-by-side reading of the captured terms.
Kalshi and Polymarket International read 27 October 2026; Polymarket US read 31 October 2026.
Three venues ask a question that sounds identical: which party will win the Senate, and which will win the House. On most nights the answers will match. They are still different contracts. Kalshi pays on who leads each chamber on 1 February 2027, and can settle early on media calls. Polymarket International and Polymarket US pay on seats won, and can wait for runoffs and for independents to say whom they caucus with. Their counting rules read almost the same. They differ in the sources they name and in who decides a dispute: Kalshi itself, UMA's oracle and token holders, or the officers of the Polymarket US exchange.
That matters for anyone holding one against another. The contracts can settle weeks apart, which ties up capital, and in edge cases (a 50–50 Senate, a member switching parties after the election, a delayed runoff) they measure different things.
The Senate
| Term | Kalshi | Polymarket International | Polymarket US |
|---|---|---|---|
| What decides the outcome | The party of the President pro tempore of the Senate, as recorded on congress.gov at 10:00 AM ET on 1 February 2027. | The party that wins a majority of the Senate's voting seats. At 50–50, the party that holds the Vice Presidency. If still ambiguous, the party of the first President pro tempore of the 120th Congress. | The party that wins a majority of the Senate's voting seats. If no party has a majority, the party that wins half of the seats and holds the Vice Presidency. If still ambiguous, the party of the first selected President Pro Tempore of the Congress that convenes after the election. |
| Who decides | Kalshi. Its CONTROL terms name congress.gov as the source agency and say Kalshi may, at its sole discretion, start its Market Outcome Review Process before settlement (Rule 6.3(c) of its rulebook). | UMA's optimistic oracle: anyone can propose an outcome, with a 2-hour challenge period. If a proposal is disputed twice, UMA token holders vote. | The exchange. Under Rule 10.4 of the Polymarket US Rulebook (version dated 30 September 2026), named officers may review a contract before settlement, the exchange may determine the final outcome, and its determinations are final. |
| Settling early | Allowed once at least 4 of 8 named media desks call the winner and none contradicts: NYT, AP, Decision Desk HQ, CNN, Fox News, NBC News, CBS News and ABC News. | Not tied to a set of media desks. Resolution sources are state electoral authorities, the US Congress and a consensus of credible reporting. | Not tied to a set of media desks. The outcome is sourced from relevant state electoral authorities and the US Senate. Unlike Polymarket International's text, it does not name a consensus of credible reporting. |
| Runoffs | Not addressed separately: the chamber leader's party on 1 February 2027 decides. | Runoffs for qualifying seats decide those seats, even when held after November. | Runoffs for qualifying elections decide the relevant seat, even if held after November 2026. |
| Independents | The terms say the exchange will also consider the caucus decisions of independent members. | Counted with the party they caucus with. The market can stay open for their announcements until 11:59 PM ET on 4 January 2027; without one, they count for no party. | Counted with the party they formally caucus with or, for newly elected members, announce they will caucus with. Settlement may be postponed until the earlier of their announcement or 11:59 PM ET on 4 January 2027; without one, they count for no party. |
| Party switches after election day | Not addressed separately: the leader's party on 1 February 2027 decides. | A member-elect's seat stays with the party under which they were elected. | A seat contested in November stays with the party under which its member was elected, even if the member-elect changes party or vacates before Congress is organized. |
| Vacant and uncontested seats | Not addressed separately: the President pro tempore's party on 1 February 2027 decides. | A seat not up for election goes to the party holding it on election day; a later switch or vacancy does not change that. A vacant seat with no November election scheduled as of 31 October 2026 goes to the party of its most recent member. | A seat not up for election goes to the party holding it on election day; a later switch or vacancy does not change that. A vacant seat with no November election scheduled as of 31 October 2026 goes to the party of its most recent member. |
| Latest settlement | Expires at 10:00 AM ET on 1 February 2027 (or earlier under the media rule) and settles no later than the next day, unless the outcome is under review. | No fixed date: when the seat count is determinable, which can wait on runoffs and, for independents, until 4 January 2027. | No fixed date in the market text: settlement can wait on runoffs held after November and, for undeclared independents, until 11:59 PM ET on 4 January 2027. The gateway lists an end date of 2 February 2027, 04:59 UTC. |
The House
| Term | Kalshi | Polymarket International | Polymarket US |
|---|---|---|---|
| What decides the outcome | The party of the Speaker of the House, as recorded on congress.gov at 10:00 AM ET on 1 February 2027. | The party that wins a majority of the House's voting seats. If no party has a majority, the party of the first elected Speaker of the 120th Congress. | The party that wins a majority of the House's voting seats. If no party has a majority, the party of the first elected Speaker of the House of the Congress that convenes after the election. |
| Who decides | Kalshi. Its CONTROL terms name congress.gov as the source agency and say Kalshi may, at its sole discretion, start its Market Outcome Review Process before settlement (Rule 6.3(c) of its rulebook). | UMA's optimistic oracle: anyone can propose an outcome, with a 2-hour challenge period. If a proposal is disputed twice, UMA token holders vote. | The exchange. Under Rule 10.4 of the Polymarket US Rulebook (version dated 30 September 2026), named officers may review a contract before settlement, the exchange may determine the final outcome, and its determinations are final. |
| Settling early | Same media rule as the Senate: at least 4 of the 8 named desks, none contradicting. | Same sources as the Senate: state electoral authorities, the US Congress and a consensus of credible reporting. | Not tied to a set of media desks. The outcome is sourced from relevant state electoral authorities and the US House of Representatives; the text does not name a consensus of credible reporting. |
| Runoffs, independents and switches | The terms say the exchange will also consider the caucus decisions of independent members. Runoffs and party switches are not addressed separately: the Speaker's party on 1 February 2027 decides. | Same rules as the Senate: runoffs count, independents count with their caucus (announcement deadline 4 January 2027), and a seat stays with the party under which its member was elected. | Runoffs decide their seats. Independents count with the party they caucus with or announce they will; the market may remain open until the earlier of their announcement or 11:59 PM ET on 4 January 2027. A seat stays with the party under which its member was elected, even if the member-elect changes party or vacates before Congress is organized. |
| Vacant and uncontested seats | Not addressed separately: the Speaker's party on 1 February 2027 decides. | Not addressed separately. | Not addressed separately. |
What to check before treating them as one position
- The measure. Chamber leadership on a date (Kalshi) and seats won under counting rules (both Polymarkets) usually agree, but they are not the same observation.
- The clock. An early media consensus can settle Kalshi within days of 3 November, while a runoff or an undeclared independent can keep either Polymarket contract open into January.
- The source. Kalshi names congress.gov and eight media desks. Polymarket International names state electoral authorities, the US Congress and a consensus of credible reporting. Polymarket US names state electoral authorities and the chamber itself.
- Who decides. Kalshi runs its own outcome review. Polymarket International resolves through UMA's optimistic oracle, with a token-holder vote if a proposal is disputed twice. Polymarket US leaves outcome review to its exchange officers, whose determinations its rulebook makes final.
- The seats nobody contests. Both Polymarket texts say how a Senate seat not up for election, or a vacant one, is counted. Kalshi does not address them separately, because it reads the chamber leader's party on 1 February 2027.
- The version. Rules can change, and Polymarket US can modify contract specifications after listing (Rulebook Rule 10.3). Check each venue's current text on the day you act; this page records what the terms said on 27 and 31 October 2026.
Sources and scope
- Kalshi contract terms for the CONTROL series: CONTROL.pdf
- Kalshi markets: CONTROLS-2026 (Senate) and CONTROLH-2026 (House)
- Polymarket markets: Which party will win the Senate in 2026? and Which party will win the House in 2026?
- Polymarket resolution process: Polymarket documentation, Resolution
- Polymarket US markets: U.S. Senate Midterm Winner and U.S. House Midterm Winner. Rule text read from the public market records for the Democratic and Republican markets of each chamber.
- Polymarket US Rulebook (version dated 30 September 2026), Chapter 1 definitions and Rule 10.4, contract outcome review: polymarketexchange.com
Kalshi and Polymarket International terms were read on 27 October 2026. On 31 October 2026 we re-read Kalshi's CONTROL terms, the Polymarket International event text and Polymarket's resolution documentation for the “Who decides” and “Vacant and uncontested seats” rows. The other rows are unchanged from 27 October. Polymarket US terms were read on 31 October 2026. This page compares contract wording only. It shows no prices and is not investment, legal or tax advice.
To compare other contracts the same way, use the contract comparison checklist or read when two event contracts are not the same contract.