L2 Isthmus Hardfork

This page outlines breaking changes related to the Isthmus network upgrade for node operators.

info

This page will be kept updated with key information about the hardfork.

• Baklava testnet activation tentatively planned on block 37277000, June 4, 2025, 15:00 UTC.
• Alfajores testnet activation tentatively planned on block 48699000, June 11, 2025, 15:00 UTC.
• Mainnet activation planned on block 38963000, June 25, 2025, 15:00 UTC.

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.

  Notable EIP's included:

  • EIP-7702: Set code transaction
  • EIP-2537: BLS12-381 precompiles
  • EIP-2935: Block hashes contract predeploy
  • EIP-7623: Increase calldata cost

• 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.

For more information on the Isthmus implementation details, please review OP's Isthmus specification.

Isthmus additionally enables the Holocene hardfork with the following changes:

• Holocene block derivation: A set of changes that render the derivation pipeline stricter and simpler, improving worst-case scenarios for the Fault Proof System and Interoperability.
• EIP-1559 configurability: The elasticity and denominator EIP-1559 parameters become configurable via the SystemConfig L1 contract, allowing the gas target and gas limit to be configured independently.

For more information on the Holocene details, please review OP's Holocene specification.