This market resolves to YES if Claude Fable 5 or its direct Anthropic successor holds the uncontested #1 spot on BOTH of the following leaderboards at 11:59 PM UTC on December 31, 2026. Otherwise, it resolves to NO.

The required leaderboards are the LMSYS Chatbot Arena Coding category (lmarena.ai) and the Arena.ai Code Arena WebDev Overall leaderboard (arena.ai/leaderboard/code/webdev).

An official tie for #1 on either leaderboard resolves to NO. Direct product line successors released by Anthropic count toward resolution. If one leaderboard becomes defunct, the remaining active leaderboard determines the outcome. If both freeze or shut down, the last archived rankings apply.

Background

Anthropic launched Claude Fable 5 on June 9, 2026, as the first widely available entry in its Mythos-class lineup. The model immediately topped multiple coding benchmarks—securing an 80.3% score on SWE-Bench Pro and claiming the top spot across Arena.ai's Code Arena: Frontend, LMSYS's Text Arena (Coding category), and other leaderboards.

The competitive landscape is rapidly evolving. Models like Z.ai's GLM-5.2 have already contested Anthropic's lead in specific categories (such as Design Arena's HTML web design leaderboard), while OpenAI’s GPT series and others continue to push frontier capabilities. This market tracks whether Anthropic's flagship coding model can maintain its crown.

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