Anthropic holds second place on the arena.ai Math board, but only just

Anthropic's Claude Opus 5 (Max) sits second on the arena.ai Text Arena math leaderboard with a score of 1533, according to the arena dataset published on October 22 and read on October 28 (style control off, Models view). Google's Gemini 4 Argon (High) leads at 1538. Anthropic also holds third and fifth, with Claude Fable 5.1 (Max) at 1532 and Claude Opus 5 (High) at 1531. Google's Gemini 3.8 Flash (High) is fourth at 1532. That depth is the main reason the forecast leans toward Anthropic being the second-best lab. Even if one entry slipped, others from the same company are bunched close behind. Only Google has an entry ahead of them, and on the lab ranking, the best entry per company is what counts. I would not treat it as settled. The gaps are a few points, and the deciding check is on Saturday, October 31 at 12:00 PM ET. Anthropic announced Claude Opus 5.5 on October 28. A launch announcement is not a leaderboard entry, and arena rows often lag releases, so I would not assume it appears in time. If it did, it could lift Anthropic to first and still leave the company ahead of the rest of the field, which would not help this outcome. A new Google or OpenAI entry could also squeeze Anthropic out of the runner-up slot. One third-party report on October 27 also lists a 1533 score and a #2 position for an Anthropic model. Its settings and snapshot are not established, so it is only a loose cross-check. The thing to watch is the next leaderboard refresh. A Claude Opus 5.5 row, or a new Google entry scoring above 1533, would most change the picture.