Arena raises $200M Series B to scale AI evaluation and alignment index

AI evaluation startup Arena announced a 200 million dollar Series B round on October 8, 2026, valuing the company at 3.1 billion dollars. The round, co led by Lightspeed Venture Partners and Khosla Ventures, coincides with the launch of Arena’s Alignment Index, a new metric for how closely AI agents follow human intent in real world use.