Arena, the startup behind one of the most watched AI leaderboards, has closed a $200 million Series B at a post-money valuation of $2.88 billion. The company has now raised approximately $450 million in total funding, following a $100 million seed round in May 2025 and a $150 million Series A in January 2026. Its commercial AI Evaluations product reached an estimated annualized run-rate of $100 million by June 2026. Arena launched the Alignment Index on October 8, 2026, a benchmark measuring AI agent safety and alignment based on more than 90,000 agent sessions across 27 different models. GPT-6.1-Sol from OpenAI leads the index with a score of 87.9, ahead of Anthropic’s Claude-Opus-5.5 at 83.2 and Grok-4.7 at 82.7.
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