Upgrade 16b: Preparing for L1 Fusaka upgrade
This page provides external-facing information about the Fusaka readiness upgrade for OP Stack chains. It summarizes scope, timelines, required actions, and resources for chain operators and partners. This upgrade is necessary for all OP Stack chains deriving from an L1 chain which is due to activate Fusaka (including Ethereum Mainnet and Sepolia). This is NOT Fusaka adoption on L2. It’s a readiness upgrade to make the Optimism protocol compatible with L1 that activates the Fusaka fork. L2 adoption will happen in a future upgrade.All of the tasks below must be performed before Fusaka activates on L1 (October 14th for Sepolia chains).
What’s included in Fusaka
Fusaka contains various breaking changes. See EIP-7607: Hardfork Meta - Fusaka for more info.For node operators
Update your node software as soon as possible after release:- Update
op-nodeto v1.14.0. See the release notes for new config flags and env variables (not necessary for chains deriving from Ethereum Mainnet, Sepolia, or Hoodi.) - Update
op-gethto v1.101603.1
Ensure your L1 beacon node endpoint can serve all blobs
Important dates: Ethereum Sepolia Fusaka hard fork: Expected October 14th, 2025 (affects chains posting data to Sepolia) Ethereum Mainnet Fusaka hard fork: Expected early December 2025 (affects chains posting data to Mainnet) For operators using an external L1 Ethereum Beacon: Before the Ethereum Fusaka hard fork, ensure your external L1 Beacon Chain RPC provider has configured their node to subscribe to all subnets. If your external L1 Beacon Chain RPC provider doesn’t subscribe to all subnets, migrate to one that does prior to these deadlines. For operators running their own L1 Ethereum Beacon Chain Node: Configure your Beacon Node with the new flag (detailed below) before the relevant Fusaka hard fork date. L1 Beacon Chain Node flags:- Lighthouse:
--supernode - Teku:
--p2p-subscribe-all-custody-subnets-enabled - Grandine:
--subscribe-all-data-column-subnets - Lodestar:
--supernode - Nimbus:
--debug-peerdas-supernode
For chain operators
Be ready to restart your batcher with the new configuration immediately after the Fusaka fork on Sepolia (Unix timestamp 1760427360 , Tue Oct 14 2025 07:36:00 )
| Component | Version | Notes |
|---|---|---|
proxyd | v4.19.0 or greater | You need to whitelist eth_blobBaseFee rpc if using proxyd for L1 load balancing |
op-batcher | v1.16.0 | OP_BATCHER_TXMGR_ENABLE_CELL_PROOFS: true or equivalent CLI flag needs to be set and the batcher restarted just after Fusaka activates on L1. |
op-node | v1.14.0 | L1 chain config must be supplied via a new flag. Not necessary for chains deriving from Ethereum Mainnet, Sepolia or Hoodi. |
op-geth | v1.101603.1 | |
op-challenger | v1.6.0-rc.3 | If deploying to a custom L1, must supply a custom L1 flag Not necessary for chains deriving from Ethereum Mainnet, Sepolia or Hoodi. |
kona-node | v1.1.2 | |
kona-host | v1.1.0-rc.3 | |
kona-client | v1.1.0-rc.3 | |
op-reth | v1.8.2 |
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/v1.7.0-rc.2. The following permissionless fault proof Sepolia chains are:Base Sepolia, Ink Sepolia, Uni Sepolia, and OP Sepolia.
OP-governed permissionless fault proof chains will have prestate update (steps 3,4, and 5) completed by Optimism.
1
Verify the new absolute prestate
2
As of upgrade 14, the 64 bit multi-threaded version of cannon is utilized.
3
The absolute prestate is generated with the op-program/v1.7.0-rc.2. You can use this new absolute prestate (
0x03f05793ed3abc475137f73b68c80593cbbf40f5d1059d2ad9b8bfcb97fa8929) for chains currently in the Superchain.4
You can verify this absolute prestate by running the following command in the root of the monorepo on the
op-program/v1.7.0-rc.2 tag:5
make reproducible-prestate
6
Upload your new preimage file
7
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 0x03f05793ed3abc475137f73b68c80593cbbf40f5d1059d2ad9b8bfcb97fa8929.bin.gz.8
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.9
Deploy new dispute game contracts
10
You will then take the absolute prestate and deploy new
FaultDisputeGame and PermissionedDisputeGame contracts with that value.11
Update the DisputeGameFactory
12
You will then need to update the
DisputeGameFactory to point to the new FaultDisputeGame and PermissionedDisputeGame contracts by calling DisputeGameFactory.setImplementation.13
Execute the upgrade
14
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.