LMSYS Chatbot Arena (@arena) · 10/9/2026, 05:36:59
Arena.ai Raises $200M Series B at $3.1B Valuation and Launches Alignment Index Based on Real-World Agent Traces
AI evaluation platform Arena.ai announced a $200M Series B round led by Lightspeed and Khosla Ventures, reaching a $3.1B valuation. Concurrently, the company released its 'Alignment Index,' built from over 62 million real-world votes and agent traces, designed to quantify frontier model safety and honesty through three key signals: Unauthorized Action, False Attribution, and Deceptive Completion.
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Arena.ai (@arena) · 2026-10-08 21
We’re incredibly proud to continue working with @thehousefund!
↳ 引用 @thehousefund (The House Fund): .@arena just raised a 3.1B valuation.
Co-led by our friends Lightspeed and Khosla Ventures, including a16z, AMP PBC, Felicis, Salesforce Ventures, 01 Advisors, Dell Technologies Capital, Endeavor Catalyst, The House Fund, and others.
We're proud investors since the first round, and excited to double down into this round.
Since the Series A:
- $100M+ in annualized revenue
- 350M sessions across the platform -7M Agent Arena sessions in under five months
- 62M votes across text, vision, code, search, image, and video
- Users in 150+ countries
Alongside the raise, Arena released its Alignment Index, built from real-world agent traces. It starts with three signals across 20+ frontier models: Unauthorized Action, False Attribution, and Deceptive Completion.
It’s worth remembering where this started. Arena launched in 2023 as a research project out of UC Berkeley. It became a company in 2025.
Today, it’s how the AI industry checks its own work.
Congrats to @ml_angelopoulos, @infwinston, @istoica05, and the entire Arena team!
Berkeley research, keeping AI honest. Go Bears!
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