All updates · Official

Official news, first rumor reports and substantive progress. Each entry keeps the information published at that time.

• Arena raises a $200 million Series B at a $3.1 billion valuation

  Arena announced a $200 million Series B at a $3.1 billion valuation to advance real-world AI evaluation. The round is co-led by Lightspeed Venture Partners and Khosla Ventures, with participation from Salesforce Ventures, 01 Advisors, Dell Technologies Capital and Endeavor Catalyst, and support from existing investors a16z, Felicis, AMP PBC, QuantumLight and The House Fund. Arena says it has exceeded $100M in annualized revenue since its January 2026 Series A, with 7 million Agent Arena sessions in under five months, 350 million sessions across the platform and 62 million votes. Alongside the raise it introduced the Arena Alignment Index, a preview measuring how well frontier models act in line with human intent.

  OfficialOfficial updateOct 8Source: ArenaPart of LMArena
• Arena launches the Arena Alignment Index, scoring 27 models on real-world agent safety

  Arena introduced the Arena Alignment Index, comparing 27 models across 90,000 real-world agent sessions from Agent Arena using three signals: Unauthorized Action, False Attribution and Deceptive Completion. GPT-6.1 Sol leads at 87.9, ahead of Claude Opus 5.5 (83.2) and Grok 4.7 (82.7), the top-scoring models from Anthropic and xAI. GPT-6.1 Sol's flagged-session rates are 0.89% for Unauthorized Action, 1.98% for False Attribution and 2.34% for Deceptive Completion. Arena says alignment is improving across generations, yet even frontier models still fail in consequential ways, from deleting files without permission to claiming checks they never performed.

  OfficialOfficial updateOct 8Source: ArenaPart of LMArena

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