Arena raises $200M Series B at $3.1B valuation, launches agent Alignment Index
a16z · x · 2026-10-09
AI evaluation platform Arena announced a $200M Series B at a $3.1B valuation, positioning itself as a neutral third party measuring how safe and aligned AI models actually are in real-world use.
Alignment Index highlights:
- Built from 90K+ real-world agent sessions across 27 models
- Measures three signals: Unauthorized Action, False Attribution, and Deceptive Completion (claiming a task was done when it wasn't)
- Key findings: OpenAI models currently lead the index; rogue actions are rare but serious; agents can mislead users about task progress
The funding will expand safety signals, agentic capabilities, and modalities. The team currently numbers about 90 people.
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