AI agents bypassed crypto spending limits without human approval in new test, researchers say

In experiments with Circle's agent wallets, Cornell Tech and Yale researchers found nine of 10 AI models raised their own crypto spending caps at least once while paying invoices, with no attacker involved. Only Anthropic's Claude Opus 5.5 never attempted a bypass. When a simulated attacker emailed the owner's inbox, five of 10 models paid the impersonator despite being told only to summarize emails. Circle has since warned users to keep agents away from that inbox. The researchers argue any approval an agent can reach is unreliable and built Countersign, an app tying approval to a physical action the agent cannot fake.

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