Arena Announces a $200 Million Series B at a $3.1 Billion Valuation to Advance Real-World AI Evaluation

Arena, the official AI ranking and LLM leaderboard, led by Anastasios Angelopoulos, Wei-Lin Chiang, and Ion Stoica, has announced a $200 million Series B at a $3.1 billion valuation to continue on its mission to measure and advance the AI frontier for real-world use. In parallel, arena is announcing the release of its Alignment Index, which measures how AI can deviate from human values in the real world.

Arena’s Series B, co-led by Lightspeed Venture Partners and Khosla Ventures, will support its mission to independently evaluate AI safety, alignment, and real-world performance. The company has evolved from human-preference evaluations and factuality assessments to Agent Arena, which measures AI agents across tasks such as coding, document analysis, and creative writing. Its new Alignment Index aims to assess whether increasingly capable AI systems can be trusted in real-world applications.

Arena reports 7 million Agent Arena sessions within five months, 350 million sessions across its platform, 62 million user votes, and a global audience spanning 150+ countries. With over 1,000 model evaluations and 375,000 open-source data points, the company is expanding beyond capability rankings with its new Alignment Index to assess AI agents’ real-world trustworthiness and alignment.

Arena’s Alignment Index introduces three real-world AI safety signals: Unauthorized Action, False Attribution, and Deceptive Completion. The initial assessment covers 20+ frontier models, using actual agent traces to evaluate whether systems act beyond user instructions, misrepresent user-provided information, or falsely claim task completion. Arena plans to expand the evidence-based leaderboard over time, complementing its existing agent capability rankings with independent assessments of alignment and trustworthiness.