Upgrade notice for ArbOS 61
ArbOS 61 "Elara" is active on Arbitrum Sepolia. The ArbitrumDAO approved it for Arbitrum One and Arbitrum Nova, where it activates on Thursday, August 20, 2026, at 17:00 UTC.
Node operators must upgrade to Nitro v3.11 or higher to continue syncing these chains.
- Docker image: offchainlabs/nitro-node:v3.11.0-a618155
- Release notes: https://github.com/OffchainLabs/nitro/releases/tag/v3.11.0
Actions required for node operators
Sepolia network
ArbOS 61 activated on the Arbitrum Sepolia chain on Monday, June 29, 2026, at 15:00 UTC.
Arbitrum One and Arbitrum Nova
The ArbitrumDAO approved ArbOS 61 for Arbitrum One and Arbitrum Nova in a Constitutional onchain vote. After the waiting periods and phases set out in the ArbitrumDAO Constitution, ArbOS 61 activates on both chains on Thursday, August 20, 2026, at 17:00 UTC.
Complete the upgrade before that date. The Arbitrum DAO network upgrades table records the exact activation time after the upgrade executes.
Important dates
The following dates are relevant for Arbitrum chain operators.
| Date | Network upgrade | Affected audience |
|---|---|---|
| Monday, June 29, 2026 at 15:00 UTC | Arbitrum Sepolia upgrade to ArbOS 61 | Node operators running Arbitrum Sepolia |
| Thursday, August 20, 2026 at 17:00 UTC | Arbitrum One/Nova upgrade to ArbOS 61 | Node operators running Arbitrum One/Nova |
Context
ArbOS 61 "Elara" builds upon ArbOS 51 "Dia". It makes two changes to Arbitrum One and Nova: it raises the Stylus contract code size limit to 96 KB, and it adds a BaseFeeManager contract that manages the minimum L2 base fee.
ArbOS 61 also ships two features that stay disabled on Arbitrum One and Nova, for the convenience of other Arbitrum chains: an Alternative Data Availability (AltDA) Layer API, and optional compliance transaction filtering. A chain owner must enable each one explicitly.
To learn how to build a custom DA provider against the new API, refer to How to integrate with the DA API. To learn how transaction filtering works, refer to Compliance filtering.
ArbOS 61 corrects two interacting bugs in the gas refund logic that were found while testing ArbOS 60 on Arbitrum Sepolia. The fixes change the State Transition Function (STF), so they required a new ArbOS version. ArbOS 60 never activated on Arbitrum One or Nova, so neither chain was affected.
ArbOS 61 passed a Snapshot temperature check and then a Constitutional onchain vote, which closed on August 1, 2026. To learn more about the proposal, refer to the ArbOS 61 Elara AIP.