Best AI Model Odds: Polymarket's Favourite a Week Out Won 21 of 22 Month-End Checks

Polymarket runs a market every month on which company will have the top model on the LMArena text leaderboard when it is checked at 12:00 Eastern on the last day. Over 22 month-end checks from December 2024 to September 2026, the company with the highest price a week before the check won 21 times. A day before, the favourite won all 22.

The one miss came from a release. On 24 March 2025, a week before the check, xAI was 92.5% to hold the top spot at the end of the month and Google was 5.2%. Google released Gemini 2.5 Pro on 25 March, it went straight to first place, and between 14:22 and 16:57 UTC that day Google's price went from 15.0% to 86.4%.

Three companies have held the top spot at a month-end: Google 13 times, Anthropic 8 times in a row from February 2026, and xAI once, in February 2025. Prices are Polymarket's public Yes prices; the winners are the markets' settled results.

The table shows the favourite and its price 14 days and 7 days before each check, and the winner's price a day before. The median price of the eventual winner a week out was 96.3%.

The markets have changed their wording over time, from the model to the company, and their source, from lmarena.ai to arena.ai. Each settled on the top model of the text leaderboard with style control off at its stated check time.

Download table figures:CSVJSON with sources

For most of March 2025 the market expected xAI to keep the top spot it had taken in February. In the midnight UTC readings xAI rose from 54.5% on 11 March to 92.5% on 23 March, while Google fell from 6.5% to under 1%. Google climbed to 13.1% late on 24 March. On 25 March it published Gemini 2.5 Pro and said the model debuted at first place on LMArena by a significant margin. Between 14:22 and 16:57 UTC that afternoon Google's price went from 15.0% to 86.4% and xAI's fell from 81.0% to 12.0%.

It is the only month in the record where the favourite a week before the check lost. The market had no way to price a release it did not know about; what it did was move within a day once the leaderboard changed.

Download chart figures:CSVJSON with sources

February 2025 was the first turn. Two weeks before the check Google was 81.0% and xAI 6.4%. xAI unveiled Grok 3 that week; its announcement, dated 19 February, said an early version had topped the leaderboard. In the midnight UTC readings xAI's price went from 19.9% on 18 February to 77.8% on 19 February. A week before the check it was the favourite at 79.9%, and it won.

Anthropic took the top spot at the end of February 2026. Two weeks before that check it was already the favourite at 68.3%, and 90.0% a week before. It has won every check since. The closest call was April 2026: at midnight UTC on 23 April OpenAI was 28.1%, and Anthropic was 69.0% a week before the check, before it went back above 90%.

The October 2026 market is checked at 12:00 Eastern on 31 October. At 21:16 UTC on 19 October, twelve days before, Google was 73.1% and Anthropic 25.5%, so the market expected a change at the top for the first time since February. The market for the end of 2026 had Anthropic at 51.5%, Google 40.5% and OpenAI 5.9%.

Those readings were taken before this page was published and are kept as they were, so they can be checked against the results. The live prices are in the AI race room.

Four things to keep in mind when reading the monthly market.

• The market is about one leaderboard. It settles on the top model of the LMArena text ranking with style control off, which is a measure of human preference in head-to-head chats, not of every kind of ability.
• New releases move it. Both changes the market missed or caught late came from a model released within two weeks of the check.
• A week out is informative, two weeks less so. The favourite 14 days before the check lost twice in the record, in February and March 2025.
• The company is what counts. A new model from the company already on top does not change the outcome.

The record is Polymarket's 22 monthly markets on the top AI model or company, from the check on 31 December 2024 to the check on 30 September 2026, each read at the minute 14 days, 7 days, 1 day and 1 hour before 12:00 Eastern on its check day. The winner is the market that settled Yes. Brands in the two earliest markets, Gemini, Grok, ChatGPT and Claude, are counted as Google, xAI, OpenAI and Anthropic.

The August 2026 market settled on 28 September, four weeks after its check, so its settlement time is not used here. Release dates come from the companies' own announcements.

22 months are a short record and most of them were held by one company. This page reads public prices; it is not a forecast by Vultax, not a ranking of AI models and not advice to trade.