Arbitrum Pauses New Stylus Activations in Emergency Security Action

Arbitrum’s Security Council paused new Stylus contract activations on Arbitrum One and Nova on Oct. 2, 2026, blocking new code and application upgrades that require activation while leaving already-active contracts running.

Arbitrum’s emergency action report linked the precaution to AI-assisted tooling and hand-crafted WebAssembly (WASM) programs designed to degrade chain performance. It said known Stylus bugs primarily threatened the network’s ability to keep processing transactions, rather than user funds. An accompanying developer notice stated: “No attack has occurred. No user funds are affected.”

“The Stylus pause covers Arbitrum One and Nova, with Arbitrum Sepolia following suit,” the project’s developer account said on X.

Stylus, launched in September 2024, lets developers write smart contracts in languages such as Rust. Unlike conventional Ethereum Virtual Machine (EVM) contracts, Stylus code requires a separate activation step to become executable after deployment.

The council implemented the freeze by raising the activation gas requirement to a prohibitively high level on One and Nova. That changed a configuration parameter without requiring an ArbOS upgrade, according to the report.

Active Contracts Can Be Renewed

The pause prevents activation of new Stylus code, including new versions of existing applications, and reactivation of expired contracts. Already-active contracts remain usable by anyone, and anyone can extend their expiration through the keepalive mechanism before they expire. Solidity and EVM contract deployment and execution are unaffected.

The report said the ArbOS 61 upgrade had renewed all active Stylus contracts on Arbitrum One, so none currently active there would expire before Aug. 20, 2027.

A Conditional Settlement Halt

The same emergency action installed a guard for the one-step proof used by BoLD, Arbitrum’s dispute-resolution protocol. A one-step proof checks the result of a single step of computation when validators disagree.

The new OspSoundnessGuard lets anyone submit two conflicting answers for the same step in an open challenge. Only one should be valid. If the proof contract accepts both, the guard uses a new PauseExecutor contract, which has pause-only authority, to halt Arbitrum One’s settlement to Ethereum.

If triggered, that halt would leave Arbitrum One processing transactions normally but delay unconfirmed withdrawals and other messages to Ethereum. The report said this would give the Security Council time to deploy a fix and resume the rollup.

For Stylus activations, the Foundation will work with ArbitrumDAO on when and how to reopen them. The developer notice says that process aims to preserve Stylus uses while restricting hand-crafted WASM programs; neither the notice nor the emergency report sets a reopening date.