Arbitrum has officially activated its ArbOS 61 software upgrade, introducing optional protocol-level compliance filters and expanded smart contract capacities across the layer-2 network, according to an announcement detailed by The Defiant. Deployed simultaneously on both Arbitrum One and Arbitrum Nova at 17:00 UTC on August 20, 2024, the upgrade brings a suite of structural changes designed to give developers and chain operators greater flexibility.
Compliance Filters Managed by Chain Owners
According to documentation reviewed by The Defiant, the primary feature of ArbOS 61 is a built-in transaction screening tool designed for application-specific chains built using the Orbit framework. The ability to toggle this compliance filter rests entirely with individual Orbit chain owners rather than ArbitrumDAO. On the main Arbitrum One and Arbitrum Nova networks, the filter is disabled by default, requiring network operators to manually configure its components.
Chain owners can integrate external compliance providers such as TRM Labs or Chainalysis to generate restricted address lists and enforce rules on specific transfers and contract calls. The screening process operates through two main mechanisms. First, the sequencer simulates transactions before they enter a block to catch and filter rule violations. Second, transactions entering through the upper chain’s Delayed Inbox face strict validation where state transition functions managed by an on-chain guardian force non-compliant transactions to fail. To prevent restricted users from bypassing the sequencer, addresses are stored as salted hashes rather than plain text. Furthermore, documentation recommends that operators of Arbitrum One wait at least 30 days following the activation of ArbOS 61 before implementing the feature.
Stylus Capacity Expansion and Developer Changes
For developers, the most immediate impact of ArbOS 61 is a fourfold expansion of the Stylus smart contract capacity limit. According to technical specifications outlined by The Defiant, the compressed contract code size limit increases from 24KB to 96KB, reducing the need for developers to split complex logic across multiple deployments. This adjustment applies exclusively to the Stylus execution path—which supports Rust, C, and C++—and does not affect Solidity contracts.
The upgrade also raises WebAssembly (WASM) size limits and modifies WASM multi-value support, prompting developers to review existing contracts for potential deployment impacts. Additionally, the release addresses gas refund logic errors inherited from the previous ArbOS 51 “Día” upgrade. Ahead of the network transition, node operators were required to update their software to Nitro v3.11.3 or higher to maintain consensus compatibility.
Priority Fees and Base Fee Adjustments
ArbOS 61 introduces new tools for managing transaction fees on Orbit-derived chains, though these features remain disabled by default. Network operators or DAOs can enable priority fee collection through the ArbOwner precompile, though sequencer logic must be updated separately to sort transactions using priority fee fields. Activating priority fee collection on Arbitrum One specifically requires a separate constitutional DAO vote.
Base fees on Arbitrum One are managed by a newly introduced BaseFeeManager contract. Under this framework, Offchain Labs holds the authority to adjust minimum layer-2 base fees within a DAO-approved range of 0.01 to 0.10 gwei. This delegated authority expires two years after mainnet implementation, requires public notification via the Arbitrum Forum for every adjustment, and remains subject to immediate revocation by the DAO. The upgrade itself does not automatically increase transaction fees.
Adoption Across Gaming and App-Specific Chains
The new fee and compliance tools hold particular relevance for gaming networks operating as Orbit chains, such as Xai, Sanko, and Proof of Play Apex, which utilize independent gas tokens and customized fee policies. According to data cited by egamers.io, chain operators utilize priority fee adjustments and base fee controls to stabilize transaction costs during periods of high network congestion.
The deployment followed a seven-week testnet phase on the Arbitrum Sepolia network starting June 29, 2024, after winning approval through a constitutional Arbitrum Improvement Proposal. While specialized compliance tools target niche enterprise requirements on Orbit chains, developers emphasize that broader adoption will likely hinge on everyday utility features like the expanded Stylus contract limits.
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