Iran ceasefire & Strait of Hormuz: odds, flows and oil risk
As of 2026-10-26 04:32 UTC, Polymarket prices “US-Iran ceasefire continues through...? — December 31” at 27.5%; GeoShockBoard's judgment is 20%. Our biggest gap is on a different market: “US invades Iran before 2027”. Status: Ceasefire still nominally holding. After 17 similar past shocks, oil's median move over 5 sessions was -0.84%. Market context, not investment advice.
Odds: crowd vs GeoShockBoard
| Polymarket market (exact name) | Crowd "Yes" | Ours* | Gap |
|---|---|---|---|
| US-Iran ceasefire continues through...? — December 31 US–Iran ceasefire holds through Dec 31 | 27.5% | 20% | -7.5 |
| Strait of Hormuz traffic returns to normal by December 31? Hormuz traffic back to normal by Dec 31 | 11.5% | 8% | -3.5 |
| Will the U.S. invade Iran before 2027? US invades Iran before 2027 | 18.5% | 5% | -13.5 |
What would change my mind: A dated, sequenced deal text published by a mediator (Pakistan or Qatar), or a public US statement shelving post-midterm strike plans. A US strike before 3 Nov would mean the midterm brake has failed.
Killer tests (missing data = not met; tests whose date has not arrived = pending)
| Hormuz flows recover Kpler 7-day Hormuz average ≥14,000 kbd for 2 consecutive prints (now 12,653 kbd, 23 Oct briefing; pre-war 17,147) | NOT MET |
| Ceasefire broken US air or missile strike impacting Iranian territory (Polymarket resolution definition) | NOT MET |
| Mine or sinking inside the strait Confirmed mine strike or vessel sunk inside the Strait of Hormuz | MET |
Game-theory read
War of attrition under one-sided uncertainty. Iran's resolve is private, so each tanker attack is a costly signal of its type. Its 7-day plan asks the US to move first (lift the blockade before the day-6 reopening), which Washington rejects because reopening can be reversed overnight. A deal needs simultaneous, divisible steps, such as partial blockade relief against verified transits, or a guarantor whose own payoff is hostage (Pakistan, Qatar). China, as the marginal buyer, gains from any reopening. Base case: no deal before the 3 Nov midterms, and the post-midterm window is still the main strike risk (the IDF chief reportedly sees no need to strike before Israel's 27 Oct vote, while US envoy Barrack's 'this weekend' remark is cheap talk until matched by deployments); Iran's threat to hit Gulf datacentres and cables is a bid to make the Gulf states lobby Washington against it. [inference]
- Iran: Hormuz is its only leverage that scales. Reopening too early gives up the blockade and sanctions concessions, so it holds out for a package.
- US: Wants the strait open without paying up front. Indirect talks via Pakistan and Qatar continue, with extra US terms; midterms on Nov 3 raise the cost of an oil spike.
- Israel: Election on Oct 27. Maximalist rhetoric is cheap now; the costly option (renewed strikes) waits for the post-election coalition.
- Gulf/Asia buyers: Use bypass routes (Fujairah, Red Sea) and Saudi spot cargoes. They gain from any deal and lose most from a renewed tanker war.
If it escalates: history says
| Asset | +1 session | +5 sessions | +20 sessions |
|---|---|---|---|
| Oil | +0.64% ↑59% n=17 range -7.18% to +7.26% | -0.84% ↑47% n=17 range -12.00% to +27.88% | -1.16% ↑41% n=17 range -15.53% to +55.31% |
| Gold | +0.37% ↑82% n=17 range -1.48% to +6.85% | -0.20% ↑47% n=17 range -7.18% to +6.41% | -0.81% ↑47% n=17 range -14.39% to +8.35% |
| US defense (ITA) | +1.13% ↑80% n=15 range -0.86% to +4.45% | +1.74% ↑73% n=15 range -4.24% to +9.69% | +1.08% ↑60% n=15 range -11.36% to +9.64% |
| S&P 500 | +0.04% ↑53% n=19 range -4.92% to +3.73% | -0.79% ↑42% n=19 range -11.60% to +4.44% | +1.12% ↑68% n=19 range -8.81% to +16.72% |
| VIX (pts) | +0.25 ↑53% n=19 range -5.75 to +9.92 | +1.55 ↑63% n=19 range -9.28 to +10.82 | -0.82 ↑47% n=19 range -12.34 to +11.19 |
What changed this week
- Trump (25 Oct) said there would be no strike that day and told FOX 2 Detroit the war won't end until the US is satisfied Iran has no nuclear-weapons capability: 'I'm a longterm person; I'm not a short term person.' source T3
- Qatari mediators visited Tehran on 25 Oct; FM spokesman Baghaei says messages continue to pass to the US via intermediaries and the window on diplomacy is not closed, but no Iranian accepts 'complete surrender'. source T2
- Iran's ambassador to Pakistan (24 Oct, per AP) said Tehran offered via Islamabad to reopen Hormuz if the US lifts its blockade; IRGC-linked Tasnim denied any 'strait for blockade' swap and cited seven standing conditions. source T3
- CENTCOM's Adm. Cooper flew over the strait on 25 Oct; CENTCOM says it supported 3,000+ transits in six months and that main shipping routes remain clear of IRGC mines. source T3
- Trump (24 Oct): the US 'could strike Iran tomorrow, or strike a beautiful deal'; US military options are reported ready pending White House authorization. No strike announced as of this refresh. source T2
- SNSC secretary Mohsen Rezaei: Iran will not reopen Hormuz or resume talks until seven new conditions conveyed via mediators are implemented; warns cables, regional data centers and AI facilities could be targeted if war resumes. source T3
Change log
- 2026-10-22: Crowd odds only (v2) → First GeoShockBoard weights and killer tests published. v3 schema: own weights, falsifiable killers, change log
- 2026-10-23: US–Iran ceasefire holds through Dec 31: 30 → 20. Detailed post-midterm US–Israeli strike plans reported; Trump says action 'fairly soon'; IMO confirms a sinking inside the strait.
FAQ
What are the Polymarket odds for “US–Iran ceasefire holds through Dec 31”?
As of 2026-10-26 04:32 UTC, the Polymarket market “US-Iran ceasefire continues through...? — December 31” priced Yes at 27.5%. Prices are trade-implied probabilities and change continuously.
What is GeoShockBoard's own call?
US–Iran ceasefire holds through Dec 31: 20%; Hormuz traffic back to normal by Dec 31: 8%; US invades Iran before 2027: 5%. These are GeoShockBoard judgments, logged on the track record and scored at resolution.
What would change the outlook?
A dated, sequenced deal text published by a mediator (Pakistan or Qatar), or a public US statement shelving post-midterm strike plans. A US strike before 3 Nov would mean the midterm brake has failed.
Which tests are being watched?
Hormuz flows recover: not met. Ceasefire broken: not met. Mine or sinking inside the strait: met. Missing data counts as not met; tests whose date has not arrived are pending.
How did oil move after similar past shocks?
Across 17 past strike exchange and war outbreak events since 1990, oil's median move over 5 sessions was -0.84% (range -12.00% to +27.88%); it rose in 47% of cases. Past reactions do not predict future ones.
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