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) and the Mainnet Superchain will be activated at Fri May 9 2025 16:00:01 UTC (1746806401). This is for all chains who have opted into the hard fork inheritance behavior.

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 must 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. Additionally, chain operators must update op-batcher to v1.12.0 (opens in a new tab) and must update op-challenger to v1.4.0 (opens in a new tab).

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

For permissionless fault proof enabled chains

Chains running permissionless fault proofs will need to deploy new dispute game contracts with new absolute prestates. The new 64 bit version of cannon will be utilized moving forward. The Sepolia Superchain, will utilize op-program/v1.6.0-2 (opens in a new tab). The following permissionless fault proof Sepolia chains are: Base Sepolia, Ink Sepolia, and OP Sepolia.

Verify the new absolute prestate

As of upgrade 14, the 64 bit multi-threaded version of cannon is utilized.

The absolute prestate is generated with the op-program/v1.6.0-rc.2 (opens in a new tab). You can use this new absolute prestate (0x03682932cec7ce0a3874b19675a6bbc923054a7b321efc7d3835187b172494b6) for the following chains:

Sepolia: Base, Creator Chain, OP, Metal, Mode, Zora, Ethernity, Unichain, Ink, and Minato (Soneium)

You can verify this absolute prestate by running the following command (opens in a new tab) in the root of the monorepo on the op-program/v1.6.0-rc.2 tag:

make reproducible-prestate

You should expect the following output at the end of the command:

Cannon Absolute prestate hash: 
0x03513e996556589f633fe1d38d694f63bc93cca5df559af37631b30875a829e9
Cannon64 Absolute prestate hash: 
0x03682932cec7ce0a3874b19675a6bbc923054a7b321efc7d3835187b172494b6
CannonInterop Absolute prestate hash: 
0x0399cfb018011977a027d1e7a85eb7ff101aec9bfc7d6500abac944c47a4581f

Upload your new preimage file

During the previous step, you also generated the preimage of the absolute prestate, which is basically the op-program serialized into a binary file. You'll find that new file at optimism/op-program/bin/prestate-mt64.bin.gz. Rename that file to have the absolute prestate hash as the filename so it looks like 0x03682932cec7ce0a3874b19675a6bbc923054a7b321efc7d3835187b172494b6.bin.gz.

Upload that file to where you're storing your other absolute preimage files. This should be the location where you're pointing your --cannon-prestates-url at. The op-challenger will grab this file and use it when it needs to challenge games.

Deploy new dispute game contracts

You will then take the absolute prestate and deploy new FaultDisputeGame and PermissionedDisputeGame contracts with that value.

Update the DisputeGameFactory

You will then need to update the DisputeGameFactory to point to the new FaultDisputeGame and PermissionedDisputeGame contracts by calling DisputeGameFactory.setImplementation.

Execute the upgrade

Once your op-challenger is ready with the new preimage, you can execute the "Set Dispute Game Implementation" transaction. Please simulate and validate that the expected output prior to executing the transaction.

The new op-program release that contains the Mainnet activation timestamps will be available soon.

For node operators

The Mainnet node binaries will be available soon. The following versions are for the Sepolia Superchain activation.

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:

The override flag for op-node was missed and will be added in the mainnet release. If you utilize the override flags, please just set the activation time in the rollup configuration file.

⚠️

If you use custom genesis chain configuration, you need to set the pragueTime to the same value as the isthmusTime. It is not automatically set, this happens by default for chains using the network flags and also when using the override flags.

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