Arbitrum’s Security Council temporarily blocked new Stylus contract activations on Arbitrum One and Nova in an emergency action on October 2, with linked transaction records showing execution at about 15:30 to 15:31 UTC. The restriction affects new programs, application updates and reactivations that require fresh activation, but does not stop already-active Stylus applications or ordinary Solidity contract deployment and execution. Arbitrum said increasingly sophisticated AI-assisted attacks involving hand-crafted WebAssembly programs prompted the precaution. Known Stylus bugs primarily threaten chain liveness, including denial-of-service risks, and no attack permitting theft of user funds had been discovered. The Council raised the activation gas requirement to a prohibitively expensive level without upgrading ArbOS. A separate safeguard on Arbitrum One’s BoLD one-step proofs could suspend settlement to Ethereum if conflicting proofs are accepted, delaying unconfirmed messages such as withdrawals while One continues processing normally. The Arbitrum Foundation will work with ArbitrumDAO on when and how to restore activations.