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Notices (README)
Upgrade 15: Isthmus Hard Fork

Upgrade 15: Isthumus Hard Fork

This page outlines breaking changes related to the Isthmus network upgrade for chain operators and node operators. The upgrade proposal is available here (opens in a new tab) and the governance vote is available here (opens in a new tab).

If you experience difficulty at any stage of this process, please reach out to developer support.

The Isthmus hard fork for the Sepolia Superchain will be activated at Thu Apr 17 16:00:00 UTC 2025 (1744905600). This is for all chains who have opted into the hard fork inheritance behavior. The activation for the Mainnet Superchain will be decided after Pectra activates on Ethereum. This time is still to be determined. The last tentative timeline from the Ethereum All Core Devs call is May 7th (from the call on Thursday, April 3rd).

What's included in Isthmus

Isthmus contains these main changes:

  • Implement Prague features on the OP Stack: This includes the EIPs that are relevant to the L2 that are being added to Ethereum with its Pectra activation. Learn more about this here (opens in a new tab).
  • L2 Withdrawals Root in Block Header: This lowers the lift for chain operators by allowing them to run a full node to operate op-dispute-mon making it easier to guarantee the security of the fault proofs for the chains in the Superchain as the number of chains scales. Learn more about this here (opens in a new tab).
  • Operator Fee: A new component to the fee formula for the OP Stack which is a first step towards better resource pricing. This improves the OP Stack ability to support chains using Alt-DA or using ZK proving. Learn more about this here (opens in a new tab).

For more information on the Isthmus implementation details, please review Isthmus specification (opens in a new tab).

For chain operators

Chain operators should upgrade their nodes ahead of the activation times to a release that contains the Isthmus changes and has the activation times for their chains baked in, or set the activation times manually via overrides. The details are outlined in the node operator section below.

In addition to this, the L1 smart contract upgrades in upgrade 14 are required to utilize this new functionality.

For permissionless fault proof enabled chains

In addition to the upgrade 14 contract updates. Chains running permissionless fault proofs will need to deploy new dispute game contracts with new absolute prestates. The new op-program release that contains the activation timestamps will be available soon.

For node operators

Node operators will need to upgrade to the respective Isthmus releases before the activation dates.

These following steps are necessary for every node operator:

Update to the latest release

The releases are for the Isthmus Sepolia Superchain activation. Mainnet releases will be cut when the activation timestamp has been determined.

Configure the Isthmus activation date

⚠️

If you are operating a node for an OP Chain that has opted into the hardfork activation inheritance behavior (opens in a new tab) and are utilizing the network flags, the Isthmus activation date is part of the op-node and op-geth nodes. So, no action is needed for the sequencer after upgrading to the latest release. Please skip to Step 3: Verify Your Configuration.

The following chains are included but are subject to change: Base Sepolia, Creator Chain Testnet, Ethernity Sepolia, Ink Sepolia, Lisk Sepolia, Metal Sepolia, Mode Sepolia, Minato (Soneium) Sepolia, OP Sepolia, Unichain Sepolia, and Zora Sepolia.

For node operators of not using the hardfork activation inheritance behavior (opens in a new tab), you will need to manually configure the activation. This can be done one of two ways:

  • Option 1: Set the activation time in the rollup.json for op-node. You will still need to set the override.isthmus flag in op-geth if you use this option. Please note that the chain configuration file is subject to a stricter format and needs to contain the chain_op_config outlined in the op-node/v1.11.0 release notes (opens in a new tab).
  • Option 2: Set the activation time via overrides (CLI) in both op-node and op-geth. These will need to be set on op-node and op-geth for the sequencer and all other nodes.

Verify Your Configuration

Make the following checks to verify that your node is properly configured.

  • op-node and op-geth will log their configurations at startup
  • Check that the Isthmus time is set to activation-timestamp in the op-node startup logs
  • Check that the Isthmus time is set to activation-timestamp in the op-geth startup logs