Arbitrum Pauses New Stylus Contract Activations in Emergency Security Action

Arbitrum Blocks New Stylus Activations Over Security Concerns

Arbitrum's Security Council paused new Stylus contract activations on Arbitrum One and Nova on Oct. 2, 2026. The move blocks new code and application upgrades that need activation, while allowing already-active contracts to keep running.

The council linked the precaution to AI-assisted tooling and hand-crafted WebAssembly (WASM) programs designed to degrade chain performance. The emergency action report stated that known Stylus bugs mainly threaten the network's ability to process transactions, not user funds. An accompanying developer notice said: "No attack has occurred. No user funds are affected."

What the Pause Covers and What Does Not

• New Stylus contract activations are frozen on Arbitrum One and Nova. Arbitrum Sepolia followed suit.
• Active contracts remain usable and can be renewed 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 will expire before Aug. 20, 2027.

Emergency Guard Could Pause Withdrawals to Ethereum

The same emergency action installed a conditional guard for BoLD, Arbitrum's dispute-resolution protocol. The new OspSoundnessGuard lets anyone submit two conflicting answers for the same computation step in an open challenge. Only one should be valid.

If the proof contract accepts both answers, the guard uses a PauseExecutor contract to halt Arbitrum One's settlement to Ethereum. That 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.

When Will Stylus Open Again?

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

What Is Confirmed

Arbitrum's Security Council officially paused new Stylus activations on Oct. 2, 2026. No attack has occurred. No user funds are affected. The freeze applies to Arbitrum One, Nova, and Sepolia.

What Is Still Unclear

The reopening timeline for Stylus activations has not been announced. It is also unconfirmed whether any specific exploit triggered the action or if this is purely precautionary.

Why This Matters

Stylus, launched in September 2024, lets developers write smart contracts in languages such as Rust. It has become a popular way to build on Arbitrum. Stopping new activations limits what developers can do, but keeps existing projects running while the council addresses potential vulnerabilities.

Sources

• The Defiant