ArbOS 51 activation on ArbSepolia

On Monday, December 1, 2025 at 17:00 UTC, ArbOS 51 will activate on the Arbitrum Sepolia chain.

Action required

Arbitrum Sepolia node operators must upgrade to Nitro v3.9.3 ahead of this 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

Context

ArbOS 51 is a follow-up to ArbOS 50 that fixes issues with the Pricing Framework. ArbOS 50 was previously activated on Sepolia, but the Gas Target & Pricing Framework changes remained disabled pending this fix. ArbOS 51 now completes that work.

Upstream governance items (ArbOS 50 + Gas Target & Pricing Framework) are being bundled into a single on-chain vote. Both components have passed Snapshot temperature checks, with the Tally vote expected to open on or around December 4, 2025.