How much did the SCOTUS prediction market move after the Ninth Circuit ruling?

The Polymarket contract on the Supreme Court accepting a sports event contract case by 31 December 2026 went from 29 cents at 17:00 UTC on 28 August 2026 to 55.5 cents at 18:00 UTC, a 26.5 cent move in one hour. It peaked at 58 cents at midnight UTC and was 51 cents on 1 September.

Did the October market move too?

No. The contract on the Court accepting a case by 31 October 2026 closed at 11.5 cents on both 27 and 28 August. Its entire range on the day of the ruling was inside the previous week’s range. It has since drifted to 5.5 cents as the deadline approached, not on any news.

Why would the odds of the outcome move but not the odds of the date?

Because the circuit split is an argument about whether the Court should take the case, while the calendar is a function of certiorari mechanics — petition, up to thirty days for a response, distribution, conference. That sequence does not reliably complete within nine weeks of an opinion being filed.

Are these prices probabilities?

Not exactly. They are prices for a contract that pays one dollar on YES, so they behave like probabilities, but they also carry spread and inventory effects. In markets this thin the gap between price and belief is wider than usual.

How thin are these markets?

Lifetime volume is about $15,300 on the December contract and about $890 on the October contract. A third contract in the same group, with a 31 July deadline, took about $960,000 in volume and resolved No.

Yes. The hourly series is published as a CSV linked on the page, the source endpoints are named in the methodology, and you are welcome to reproduce, check or contradict it. Attribution to BetG8 is appreciated and not required.

The market repriced the Supreme Court in one hour — and moved the calendar by zero

Explainer · Updated September 1, 2026 · 18+ · Not legal advice · By BetG8 Editorial · Prediction Markets

On Friday 28 August 2026 the Ninth Circuit held that Kalshi’s sports event contracts are not swaps under the Commodity Exchange Act, and that states may enforce their gambling laws against them. That created a direct split with the Third Circuit, which went the other way in April. Almost every outlet covering it landed on the same sentence: this is going to the Supreme Court.

There is a market on that. Two of them, in fact. They did not agree with each other, and the disagreement is the part nobody has written down.

The finding: In the hour the opinion landed, the market on the Supreme Court accepting a sports event contract case by 31 December 2026 went from 29¢ to 55.5¢ — a 26.5¢ move, up 91%, in sixty minutes. The market on the same court accepting the same case by 31 October 2026 closed that day at 11.5¢, exactly where it had closed the day before. The ruling roughly doubled the odds of the outcome and moved the odds of the near-term timeline by nothing. Download the full hourly series (CSV, 289 rows).

Hour by hour, 28 August 2026

All times UTC. The opinion in No. 25-7516 was filed on the morning of 28 August, Pacific time.

Hour (UTC)	“SCOTUS accepts by 31 Dec 2026”	“… by 31 Oct 2026”
15:00	29.0¢	11.5¢
16:00	29.0¢	11.5¢
17:00	29.0¢	11.5¢
18:00	55.5¢	11.5¢
19:00	54.5¢	11.5¢
20:00	55.0¢	11.5¢
21:00	57.0¢	11.5¢
22:00	57.5¢	11.5¢
23:00	57.5¢	11.5¢
00:00, 29 Aug	58.0 (peak)¢	11.5¢
01:00, 29 Aug	49.5¢	12.0¢
06:00, 29 Aug	52.5¢	12.5¢

The December contract had traded in a 29–31¢ band for six straight days before the ruling, and spent the entire morning of 28 August at 29¢. Then one hour took it to 55.5¢. It drifted up to 58¢ by midnight UTC, gave back eight and a half cents in the next hour, and has sat between 49.5¢ and 52.5¢ since. It was 51¢ at 06:04 UTC on 1 September.

The number that did not move

The October contract is the one worth staring at. It closed 27 August at 11.5¢. It closed 28 August at 11.5¢. Its entire range on the day of the ruling — 8¢ to 11.5¢ — sits inside the range it had already traded the previous week. A ruling that nearly doubled the December number left the October number untouched.

That is not indifference. It is the market separating two questions that the coverage merged into one. “Will the Supreme Court take this?” and “Will the Supreme Court take this in the next nine weeks?” are different questions, and only the first one is about the strength of the circuit split.

The second is about paperwork. A losing party files a petition for certiorari. The other side gets thirty days to respond, extendable. The petition is distributed, then conferenced. Even on an unusually fast track, that sequence does not reliably finish inside two months of the opinion being filed. The market appears to know this, and it priced accordingly within the same hour it repriced everything else.

The gap has widened since. As of 1 September the December contract is 51¢ and the October contract is 5.5¢. Taken at face value, that puts roughly nine-tenths of the market’s December probability mass in November and December rather than in the next eight weeks — 5.5 divided by 51 is about 11%, and the remainder is the back end of the year.

Daily summary, 20 August to 1 September

Open, high, low and close are taken from hourly midpoints, in cents.

Date (UTC)	Dec O	Dec H	Dec L	Dec C	Oct C
20 Aug	43.5	44.0	35.5	35.5	15.5
21 Aug	35.0	39.0	35.0	39.0	13.5
22 Aug	39.0	39.0	30.5	30.5	10.5
23 Aug	30.5	30.5	30.5	30.5	9.0
24 Aug	30.5	30.5	30.5	30.5	10.5
25 Aug	30.5	31.0	30.5	30.5	11.0
26 Aug	30.5	31.0	30.5	31.0	9.5
27 Aug	31.0	31.0	29.5	29.5	11.5
28 Aug	29.5	57.5	29.0	57.5	11.5
29 Aug	58.0	58.0	49.5	50.0	8.0
30 Aug	50.0	52.0	50.0	52.0	11.0
31 Aug	52.0	52.0	50.5	52.0	6.5
1 Sep	52.0	52.0	51.0	51.0	5.5

Note the rows above the ruling. The December contract had already been falling all week, from 43.5¢ on 20 August to 29.5¢ on 27 August. Whatever the market believed about a Supreme Court case before Friday, it was believing it less each day. The opinion did not accelerate a trend. It reversed one.

Methodology

We would rather you check this than trust it.

Source. Polymarket’s public CLOB price-history endpoint, clob.polymarket.com/prices-history, queried at 60-minute fidelity for the YES token of each market. Market metadata from gamma-api.polymarket.com.
Markets. “SCOTUS accepts sports event contract case by October 31, 2026?” and “… by December 31, 2026?”, both in the same Polymarket event group. “Accepts” means a grant of certiorari under the market’s own resolution criteria, not a decision on the merits.
Window. 20 August 2026 06:00 UTC to 1 September 2026 06:04 UTC. 289 hourly observations for the December market, 287 for the October market.
Prices. Cents per share of a contract that pays $1 on YES. They are prices, not probabilities — they embed spread, inventory and whatever the last trader was willing to pay. We report them as prices throughout.
Timestamps. UTC throughout. The endpoint returns the last observation at query time rather than on the hour, which is why the final row is 06:04 rather than 06:00.
Reproducing. The CSV is the raw pull, unsmoothed and unedited: scotus-repricing-aug-2026.csv. If your numbers differ from ours, ours are wrong and we would like to know.

The liquidity caveat, stated plainly

These are thin markets, and any honest reading has to start there. Lifetime volume on the December contract is about $15,300. On the October contract it is about $890. A single determined trader can move a book that size, and the 8.5¢ give-back in the hour after the peak is consistent with exactly that.

There is a third contract in the same group, and it is the one that carries the money: “SCOTUS accepts sports event contract case by July 31, 2026?” took about $960,000 in volume and resolved No. Roughly 98% of everything ever traded in this event family sat on a deadline that came and went. That is worth holding in mind before treating the two live contracts as a wisdom-of-crowds signal. They are a small number of people with real money on a narrow legal question — which is more than most commentary has, and much less than a poll.

What this is and is not

It is a record of how a market that trades this question priced a specific piece of news, at hourly resolution, with the raw data attached. It is not a forecast, not advice, and not a claim that the market is right. The Supreme Court has taken cases the market thought it would not, and passed on cases the market thought it would.

What it does show is a distinction worth borrowing: after 28 August, the case for review got much stronger and the case for speed did not change at all. Coverage that treats “headed to the Supreme Court” as a single event is flattening two things that the people with money on it are pricing separately.

FAQ

How much did the SCOTUS prediction market move after the Ninth Circuit ruling?: The Polymarket contract on the Supreme Court accepting a sports event contract case by 31 December 2026 went from 29¢ at 17:00 UTC on 28 August to 55.5¢ at 18:00 UTC, a 26.5¢ move in one hour. It peaked at 58¢ at midnight UTC and was 51¢ on 1 September.
Did the October market move too?: No. The contract on the Court accepting a case by 31 October 2026 closed at 11.5¢ on both 27 and 28 August. Its whole range on ruling day was inside the previous week’s range. It has since drifted to 5.5¢ as the deadline approached, not on any news.
Why would the odds of the outcome move but not the odds of the date?: Because the circuit split is an argument about whether the Court should take the case, and the calendar is a function of certiorari mechanics — petition, up to thirty days for a response, distribution, conference. That sequence does not reliably complete within nine weeks of an opinion, whatever the merits look like.
Are these prices probabilities?: Not exactly. They are prices for a contract that pays $1 on YES, so they behave like probabilities, but they also carry spread and inventory effects. In markets this thin the gap between price and belief is wider than usual.
How thin are these markets?: Lifetime volume is about $15,300 on the December contract and about $890 on the October contract. A third contract in the same group, with a 31 July deadline, took about $960,000 and resolved No.
Can I use this data?: Yes. The hourly series is published as a CSV under a link on this page, the source endpoints are named in the methodology, and you are welcome to reproduce, check or contradict it. Attribution to BetG8 is appreciated and not required.