Upgrade 16a brings new operator controls and streamlined upgrade paths to the Superchain. Here’s what you need to know if you’re a chain operator.
The Rollout
When:
- Sepolia testnet: September 22, 2025
- Mainnet: October 2, 2025
Notable chains include: Base, Ink, OP, Soneium, and Unichain.
If you’re still on Upgrade 15, you can skip ahead and jump straight to 16a; you will get the latest improvements without the intermediate step.
Key Improvements
System-level feature toggles: Chain operators can now enable/disable specific features without full protocol upgrades.
Streamlined interop foundation: The withdrawal-proving architecture has been refined, creating a cleaner foundation for future interoperability features.
Flexible upgrade paths: The tooling now elegantly handles multiple upgrade scenarios, making future maintenance much smoother.
What This Means for Your Chain
More control: Feature toggles give you unprecedented flexibility in how and when you adopt new capabilities.
Safer rollouts: Test features independently without committing to full protocol changes.
Future-proofing: This architecture makes your chain more adaptable as the Superchain evolves.
Important Technical Notes
No downtime expected: The upgrade should complete without chain interruption.
Withdrawal considerations: If you’re upgrading from U15, any pending L1 withdrawals that aren’t finalized before the upgrade will need to be re-proven afterward. Users must re-submit their proof transactions.
ETHLockbox status: Chains already running U16 keep ETHLockbox support. Chains moving directly from U15 to U16a won’t get ETHLockbox until a future upgrade.
If you’re on U15: Follow the same upgrade process as outlined in the U16 documentation.
