Arbitrum’s Security Council has paused all new Stylus activations on Arbitrum One and Nova, citing increasingly sophisticated AI-assisted attacks, in an emergency action executed onchain around 15:30 UTC on October 2.
The Council announced the emergency action in its own forum report and paired it with a second measure: a permissionless guard on the BoLD one-step proof, the final step that settles Arbitrum One to Ethereum. Anyone can present two conflicting answers to the same step of an open challenge. If the one-step proof accepts both, the guard puts Arbitrum One’s settlement to Ethereum on hold until the Council deploys a fix. Arbitrum said the chain would keep processing normally during such a hold, but unconfirmed messages to Ethereum, including withdrawals, would have to wait. Installing the guard does not itself pause withdrawals.
Arbitrum attributed the pause to AI-assisted attacks involving hand-crafted WebAssembly programs built outside the standard Stylus compiler toolchain. The network says unpatched programs of that kind could work as denial-of-service vectors that impair chain liveness, and that no attack permitting theft of user funds was found. The freeze is a preemptive block ahead of upcoming ArbOS updates, and the Foundation framed it as part of an ongoing series of proactive security measures.
It is an early instance of a major Ethereum layer-2 pointing to AI-driven attack sophistication as the reason for an emergency measure. For developers, the practical effect is narrower than the word freeze suggests. Programs already activated keep executing, and keepalive renewal can extend an active program’s lifetime. New contract instances using identical program code can reuse an existing valid activation. What is blocked are fresh activations and reactivations of expired programs, which also freezes app updates that require one. Ordinary Solidity deployments are unaffected.
Activation is the separate step that makes a deployed WebAssembly program executable, and it is that step, not Stylus itself, that the gas change switched off.
When new activations resume is up to ArbitrumDAO. The Foundation said it will work with the DAO on the timeline, and no date has been given.
