US Senate 2026 — a calibrated coin-flip-plus-edge.

Calibrated ~0.54 probability Republicans retain the Senate after Nov 3 2026. Markets diverge (Polymarket ~56%, Kalshi ~50–51%); we split at ~0.54 — acknowledging near-coin-flip uncertainty with a thin Republican edge. Non-partisan, purely probabilistic.

Type · Prediction Lock · calibrated binary Locked · 2026-06-21 · ~4 months before the vote Resolves · 2026-11-03 · official certified results / AP race calls Scored · binary: Republicans retain Senate majority yes/no

P(Republicans retain Senate majority)

~0.54

calibrated · split of Polymarket ~56% / Kalshi ~50–51%

Polymarket ~56% GOP (Jun 20, $2.76M vol); Kalshi ~50–51% (down from 67%); CNBC dead heat framing. We calibrate to ~0.54 — coin-flip with thin GOP edge. Source spread is wide; confidence reflects that uncertainty.

— 1 · The Locked Call

Republicans retain the Senate — calibrated at ~0.54.

We lock a single binary claim: P(Republicans retain US Senate majority after November 3 2026 midterms) ≈ 0.54. This is a calibrated probability, not a prediction of a winner. The complementary probability (~0.46) covers a Democratic pickup of net seats sufficient to flip control.

— 2 · Why it's nail-able

Markets split widely; we anchor at ~0.54 as the best-available synthesis.

Polymarket (~56%, $2.76M volume as of Jun 20) and Kalshi (~50–51%, down from a 2025 peak of ~67%) diverge by ~5pp after vig removal — a rare market spread reflecting genuine uncertainty four months out. CNBC editorial framing confirms a dead heat. We calibrate at ~0.54, splitting the spread: thin GOP edge from structural map advantage (Democrats defending 23 seats vs 11 for Republicans), offset by a historically hostile midterm environment for the presidential party. Resolves against AP/NBC certified calls for all 34 contested seats; majority = 51+ seats.

Locked on 2026-06-21 — scored against certified Senate composition after Nov 3 2026.

RAOSCAFF locks P-24 on 2026-06-21, purely from calibrated market synthesis. Non-partisan: we forecast what the market implies, not what we prefer. Resolves against AP race calls for Senate control.

Locked: 2026-06-21 (commit timestamp on origin/main)
Resolves: 2026-11-03 — US Senate midterm results (AP / NBC certified race calls)
Source: AP / NBC News official Senate majority call (Republican ≥51 seats = YES)
Scored by: Binary: YES if Republicans hold ≥51 Senate seats post-certification; NO otherwise

Non-partisan framing throughout — we derive the probability from market synthesis, not political preference.