Arena raised a $200 million Series B at a $3.1 billion valuation. It also launched the Arena Alignment Index. The index measures how well AI models act in line with human intent. It tracks three signals: Unauthorized Action, False Attribution, and Deceptive Completion. The round was co-led by Lightspeed Venture Partners and Khosla Ventures. Arena has exceeded $100 million in annualized revenue. It has 7 million sessions in Agent Arena in under five months. The platform now has 350 million total sessions. It has collected 62 million votes across text, vision, code, search, video and image. The Alignment Index covers 20+ frontier models at launch.
What changed
Arena had raised a Series A in January 2026 to build an AI evaluation platform.
What it unlocks
Funding and launching the Arena Alignment Index to measure real-world AI alignment.
- $200M Series B
- $3.1B valuation
- 7M Agent Arena sessions in 5 months
- 350M total platform sessions
Sources