Does Anthropic keep the top AI ranking by September 21?

The race for the top spot on LMArena’s text leaderboard has basically turned into a one‑horse show this week. The weekly Kalshi contract on which company owns the number‑one position settles at 10:00 AM ET on Monday, September 21, with “Claude” at 97 cents, “Gemini” at 4 cents, and “ChatGPT” at 2 cents.

Anthropic currently occupies the top five slots on that board. Claude Fable 5.1 Max, added on September 13, sits first with a score of 1508 from 5,783 votes and a confidence interval of ±85 points. Just below it are Claude Opus 5 Max and Claude Opus 5 High at 1505, with two more Anthropic models rounding out the top five. The highest‑ranked non‑Anthropic entry is Google’s Gemini 3.8 Flash High at 1495, in sixth place, 13 points behind.

OpenAI’s newest model, GPT‑6 Astra, released on September 3, reached the text arena only on September 11 but has not even broken into the top ten. It does lead the Code arena’s WebDev board, though, but that leaderboard is irrelevant for this contract.

What matters here is one thing many overlook. A model does not appear on the text arena the day it is announced. Arena lists it only after it has accumulated enough votes to be ranked. For GPT‑6 Astra, that took eight days, while for Claude Fable 5.1 it took twelve. The fastest listing this month was Gemini 3.8 Flash, which appeared on September 2, the same day Google released it, and two weeks later it still sits sixth.

That leaves any new model shipped between now and Monday morning with at most five days to be listed, gather enough votes, and leapfrog five Anthropic models stacked at the top. Considering recent listing speeds and vote accumulation rates, that scenario looks highly improbable. 

Thus, at 97 cents, buying “Anthropic” for a 3.09% return by Monday is a low‑volatility, high‑probability trade. And despite the small return, on an annualized basis that’s 225.77%, which is extremely attractive.