Arbitrum's Security Council paused new Stylus contract activations on Arbitrum One and Nova on October 2, 2026, after flagging hand-crafted WebAssembly programs that could degrade network performance. Already-active contracts keep running, and a new guard now backstops Arbitrum's BoLD dispute system in case conflicting proofs are ever accepted.
Security Council freezes new Stylus code
Arbitrum's Security Council carried out an emergency action that paused new Stylus contract activations on Arbitrum One and Nova on Oct. 2, 2026, blocking new code and application upgrades that require activation. The Crypto Briefing report put the upgrade's timing at 11:30 EST.
The emergency action report linked the move to AI-assisted tooling and hand-crafted WebAssembly, or WASM, programs designed to degrade chain performance. It said the known Stylus bugs primarily threatened the network's ability to keep processing transactions, rather than user funds. According to The Defiant, an accompanying developer notice stated: "No attack has occurred. No user funds are affected."
Stylus, launched in September 2024, lets developers write smart contracts in languages such as Rust. Unlike conventional Ethereum Virtual Machine 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, changing a configuration parameter without requiring an ArbOS upgrade.
Active contracts keep running
The pause blocks activation of new Stylus code and reactivation of expired contracts, but already-active contracts remain usable, and anyone can extend their expiration through the keepalive mechanism before they expire. Solidity and EVM contract deployment and execution are unaffected. The ArbOS 61 upgrade had already renewed all active Stylus contracts on Arbitrum One, so none currently active there would expire before Aug. 20, 2027.
A new guard on the BoLD dispute system
The same emergency action installed a guard for the one-step proof used by BoLD, Arbitrum's dispute-resolution protocol, which checks the result of a single computation step when validators disagree. The new OspSoundnessGuard lets anyone submit two conflicting answers for the same step in an open challenge; 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, giving the Security Council time to deploy a fix and resume the rollup. The Arbitrum Foundation will work with ArbitrumDAO on when and how to reopen Stylus activations; neither the developer notice nor the emergency report sets a reopening date.
Sources: The Defiant, Crypto Briefing
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