Arena Raises $200 Million Series B and Launches Alignment Index for AI Agents

Arena said it raised a $200 million Series B at a $3.1 billion valuation and introduced the Arena Alignment Index, moving the former LMArena project further into the business of measuring how AI agents behave in real work. The round gives the evaluation company new capital at a moment when AI agents are shifting from chat responses to coding, analysis and tool-using tasks where failure can be harder for users to verify.