Upgrade notice for ArbOS 51
ArbOS 51 "Dia" will be activated on the Arbitrum Sepolia, Arbitrum One, and Arbitrum Nova chains.
Actions required for node operators
Arbitrum node operators must upgrade to Nitro v3.9.3 ahead of ArbOS 51 activation to continue syncing the chain.
- Docker image:
offchainlabs/nitro-node:v3.9.3-8bc5554 - Release notes: https://github.com/OffchainLabs/nitro/releases/tag/v3.9.3
Important dates
The following dates are relevant for Arbitrum chain operators.
| Date | Network upgrade | Affected audience |
|---|---|---|
Dec 1st 2025, 17:00:00 UTC | Arbitrum Sepolia upgrade to ArbOS 51 | Node operators for Arbitrum Sepolia |
Jan 8th, 2026, 17:00:00 UTC | Arbitrum One/Nova upgrade to ArbOS 51 | Node operators for Arbitrum One/Nova |
Context
ArbOS 51 "Dia" builds upon ArbOS 40 "Callisto" with support for the relevant EVM changes that are a part of Ethereum's Fusaka upgrade, as well as additional improvements to the gas pricing algorithm, a change to the min L2 base fee, MaxTxGasLimit allowing full block utilization, changes to instrument Nitro’s State Transition Function (STF) to price gas based on specific resource usage, native token mint/burn capabilities, and a few bug fixes.
Upstream governance items (ArbOS 50 + Gas Target & Pricing Framework) were bundled into a single ArbOS 51 on-chain vote. Both components have passed Snapshot temperature checks, and the bundled Tally vote was passed December 18, 2025.