OpenAI holds a narrow 55.5% implied probability for second-best AI agent lab by end-December 2026, just ahead of a crowded field of contenders at or near 50%, while Anthropic sits at 15.5% and Google at 12.5%. Trader sentiment reflects Anthropic’s recent Claude Opus 5.5 and Fable 5.1 releases, which lead multiple agentic benchmarks on long-horizon tasks, tool use, and computer-use execution. OpenAI’s GPT-6 Astra and GPT-5.6 variants remain competitive on browser and planning metrics, supported by persistent agent rollouts and API updates. The tight spread underscores rapid iteration across labs, with differentiation hinging on verifiable gains in multi-step autonomy, recovery from errors, and real-world deployment stability before year-end resolution.