**Claude Opus 5.5’s late-September release and benchmark leadership drive the 56.5% implied probability for claude-opus-5.5-high.** Anthropic launched the model on September 22, 2026, positioning it as matching or exceeding Claude Fable 5.1 on most agentic coding, knowledge-work, and reasoning benchmarks while costing roughly 40-60% less to run. It quickly topped the Artificial Analysis Intelligence Index and leads recent LMArena text rankings among frontier models. Traders see this combination of performance gains, efficiency, and Anthropic’s internal guidance favoring Opus 5.5 for typical workloads as likely to keep it ahead through the October 12 snapshot. Fable 5.1-max holds a smaller 10% share, reflecting its retained edge only on the most demanding long-horizon tasks. The 27.5% on Other accounts for potential gains by competing labs, though current leaderboards show Anthropic models dominating. With resolution just 12 days away, any new capability demonstrations or leaderboard shifts could still adjust these market-implied odds.