Arena, a San Francisco-based artificial intelligence evaluation company, announced on October 8, 2026, that it had raised $200 million in Series B funding at a valuation of $3.1 billion. The round was co-led by Lightspeed Venture Partners and Khosla Ventures.
The financing included participation from Salesforce Ventures, 01 Advisors, Dell Technologies Capital, Acrew Capital and Endeavor Catalyst. Existing investors, including Andreessen Horowitz (a16z), Felicis, AMP PBC, QuantumLight and The House Fund, also supported the round.
Founded in 2025 by Anastasios Angelopoulos, Wei-Lin Chiang and Ion Stoica, Arena originated from the Chatbot Arena research project at the University of California, Berkeley. Angelopoulos serves as CEO, Chiang as CTO and Stoica as chairman.
The company operates a platform for evaluating artificial intelligence models and agents based on their performance in real-world applications. Its evaluation services help AI developers and businesses assess model capabilities through human feedback, comparative testing and analysis of how AI systems complete tasks.
Arena’s platform supports evaluations across text, coding, vision, search, video and image generation. Its Agent Arena offering extends these assessments to multi-step workflows involving tool use, document analysis and other activities performed by AI agents.
Alongside the Series B announcement, Arena introduced a preview of its Alignment Index, an evaluation system designed to assess whether AI agents behave consistently with user instructions and expectations.
The index initially examines three observable behaviours: unauthorized actions, false attribution of information to users and deceptive claims that a task has been completed. Arena’s initial research compared 27 models using approximately 90,000 real-world agent sessions. The company plans to expand the system with additional evaluation measures.
Arena intends to use the new funding to expand its AI evaluation infrastructure, develop its platform and extend its research into model reliability and alignment.
The company reported exceeding $100 million in annualized revenue run rate. It also reported approximately 350 million sessions across its platform and more than seven million Agent Arena sessions within five months of that offering’s launch.
The Series B follows Arena’s $150 million Series A announced in January 2026, which valued the company at $1.7 billion. That earlier financing was co-led by Felicis and UC Investments.
The latest investment increases Arena’s reported valuation to $3.1 billion as the company broadens its activities from AI model comparisons to evaluations of agent capabilities, reliability and safety.
