Republicans win majorities in both the US Senate and House of Representatives in the 2026 midterm elections.
US midterm elections take place on November 3, 2026, determining control of both chambers of the 120th Congress.
Across 6 frontier models answering independently, the panel leans no: the median is 38%.
They do not agree: GPT puts it at 62% and DeepSeek at 22%, 40 points apart. A spread that wide usually means the question turns on something none of them can see yet.
Money disagrees. The market sits at 9%, so the models are 29 points more confident than people with cash on the outcome — one of the wider gaps in the archive.
Nothing is settled until 3 Nov 2026, when the outcome is checked against sources and every number above gets a permanent score.
- AI edge
- +29 pts
- Moved this week
- -4 pts
- Since we asked
- -2 pts
- Volume
- $3.4M
The models are sharply more confident than traders risking real money: 38% against 9%.
What each one said
-
GPTOpenAI
The outcome chiefly turns on whether Democrats can protect enough Senate seats while avoiding a national House-level backlash.
- The president's party has lost House seats in 19 of 20 midterms since 1946, making a Republican House gain the baseline.
- Senate control hinges on a small set of 2026 races; Republicans need net gains only if Democrats retain the vice presidency.
- A late recession, weak approval, or a large Democratic Senate recruitment advantage would materially shift these odds.
62% -
QwenAlibaba
Historical midterm penalty for the president's party vs. a Senate map that heavily favors Republicans in 2026.
- The 2026 Senate map has Democrats defending seats in red states (Montana, Ohio, etc.) while few GOP seats are competitive, giving Republicans a structural edge to hold…
- Historically the president's party loses House seats in midterms—average loss is ~26 seats since WWII—and with Republicans holding a slim majority, a Democratic House…
- A development that would shift this: a sharp improvement in Trump's approval or a major economic/diplomatic win that defies the typical midterm referendum dynamic, which…
58% -
GrokxAI
GOP Senate hold is likely on the 2026 map; House majority hinges on a late generic-ballot shift.
- Senate map favors GOP: 20+ Dem seats up vs few GOP, so they need only hold most of their 53; VP tiebreak unused if they stay above 50.
- House: president's party historically loses ~25 seats in first midterm; current generic ballot and Cook ratings leave GOP ~10 seats short of 218.
- A 3-point GOP generic-ballot swing in the next 6 weeks, or Dem overperformance in 4-5 toss-ups, would flip the joint probability most.
38% -
GeminiGoogle
The Senate map heavily favors the GOP, but historical midterm backlash against the White House makes holding the House difficult.
- The 2026 Senate cycle defends mostly Democratic-held seats in swing states, giving Republicans a strong shot at retaining control.
- Midterm base rates penalize the president's party in the House, where slim margins make surrendering the majority very likely.
- A major economic boom or deep Democratic division could preserve the GOP House majority, lifting odds above historical norms.
37% -
ClaudeAnthropic
House flips likely to Democrats on historical midterm swing; Senate map favors GOP holding majority.
- First-term president's party loses House in nearly every modern midterm, and Trump's approval has been weak, favoring Dem House takeover.
- Senate map in 2026 is favorable to Republicans with few vulnerable GOP seats and several red-state Dem-held seats up.
- Split outcome (Dem House, GOP Senate) is the modal scenario, making full GOP sweep of both chambers less likely than not.
30% -
DeepSeekDeepSeek
House control is a near-coinflip; Republicans need a net Senate gain, which is the binding constraint.
- Republicans must net +1 Senate seat (VP breaks 50-50); they defend Maine, North Carolina, and hold a 53-seat majority, so losses are the risk, not gains.
- House generic ballot has hovered near D+3 to D+5 through 2026, and the president's party typically loses ~25 House seats in midterms, putting the House below 50%.
- The joint probability is roughly the House odds times the Senate odds, so even a 45% House chance times a 50% Senate chance lands near 22%.
22%
6 of 6 models answered · 40 points between the highest and lowest. None was shown the market price.
Resolution criteria
This market will resolve according to the party that wins control of the United States Senate and the party that wins control of the United States House of Representatives in the 2026 United States midterm election. A party wins control of the United States Senate if it wins a majority of the chamber’s voting seats. If no party wins a majority of voting seats, the party that wins control of the chamber is the party that wins half of the voting seats and holds the Vice Presidency. If the outcome remains ambiguous after applying the above criteria, the chamber will be deemed controlled by the party with which the first selected President Pro Tempore of the Congress that convenes after the specified election is affiliated. A party wins control of the United States House of Representatives if it wins a majority of the chamber’s voting seats. If no party wins a majority of voting seats, the chamber will be deemed controlled by the party with which the first elected Speaker of the House of the Congress that convenes after the 2026 midterm election is affiliated. The following rules govern the counting of seats for determining which party wins control of the chambers. For determining
Question sourced from Polymarket on 18 Sept 2026. Forecast by google/gemini-3.8-flash, anthropic/claude-sonnet-5, openai/gpt-5.6-terra, x-ai/grok-4.6, deepseek/deepseek-v4.1-flash, qwen/qwen3.8-max-0902 via OpenRouter.