# Upgrade Proposal #15 - Isthmus Hard Fork

**URL:** <https://gov.optimism.io/t/upgrade-proposal-15-isthmus-hard-fork/9804>\
**Category:** Technical  Proposals\
**Created:** [April 2, 2025, 12:12am UTC](https://gov.optimism.io/t/upgrade-proposal-15-isthmus-hard-fork/9804 "2025-04-02T00:12:34Z")\
**Posts on this page:** 1\
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**Author:** ![0xEscanor](https://dub1.discourse-cdn.com/bc41dd/user_avatar/gov.optimism.io/0xescanor/32/11476_2.png) [@0xEscanor](https://gov.optimism.io/u/0xEscanor)\
**Post date:** [April 2, 2025, 12:12am UTC](https://gov.optimism.io/t/upgrade-proposal-15-isthmus-hard-fork/9804/1 "2025-04-02T00:12:34Z")

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### **Proposal Title:** Upgrade 15 - Isthmus Hard Fork

### **Proposal Type** : Protocol Upgrade

_ **This proposal is intended to be voted on in Cycle 35** _

_**This proposal is contingent upon the passing of [Upgrade Proposal #14](https://gov.optimism.io/t/upgrade-proposal-14-isthmus-l1-contracts-mt-cannon/9796/1)**_

### **Executive Summary**

Hi, I’m Lewej, a Technical Program Manager at OP Labs. I prepared this proposal in collaboration with Sebastian Stammler, Paul Dowman, and Ben Clabby from the OP Labs Team, Aurélien from Succinct, and Julian Meyer from Base.

Neither OP Labs nor I or any other entity mentioned represent or speak on behalf of the Optimism Foundation.

This proposal introduces the Isthmus hard fork. The features to be activated have been shared in preview posts:

- [Proposal Preview: L2 Withdrawals Root in Block Header](https://gov.optimism.io/t/proposal-preview-l2-withdrawals-root-in-block-header/9730)
- [Proposal Preview: Operator Fee](https://gov.optimism.io/t/proposal-preview-operator-fee/9715)
- [Proposal Preview: Implement Prague features in Isthmus](https://gov.optimism.io/t/proposal-preview-implement-prague-features-on-the-op-stack/9703)

### **Motivation**

Many of the EIPs in the Pectra hard fork are useful to end users and developers on the Superchain, so including features that enable new account abstraction primitives, make proofs more efficient, and other enhancements are important to release as soon as possible after L1 activation. Other features in the Isthmus hard fork enhance the node operator and dev experiences, especially for those working on Alt-DA & ZK chains.

### Impacted Stakeholders & Expected Outcomes

- **All node operators:** will be required to update node software to a new release once the L1 Pectra activation date is finalized.
- **Users and developers** : changes are backwards compatible, but this release enables new features like EIP-7702 to be leveraged on the Superchain. Some predeploy APIs are updated, see changelog [here](https://specs.optimism.io/protocol/isthmus/derivation.html#network-upgrade-automation-transactions).

### **Specifications**

- **Blockspace Charter**

- **Technical details**

- Impact Summaries

- **Precommitment impact review:**

### **Action Plan**

While this upgrade encompasses all code changes required to update to this new version of the OP Stack, one dependency is missing: the L1 Pectra activation date, which at the time of posting is not finalized. To deploy this upgrade, the L1 Pectra activation date needs to be known.

As such, a full action plan for this proposal is not prepared. Instead, we anticipate submitting a subsequent Maintenance Upgrade as a fast follow to this one, which sets the activation date and:

- Commits to a concrete payload which the Security Council can sign
- Tags the correct releases for off-chain software, inclusive of activation date, including:
  - op-node
  - op-geth
  - op-challenger
  - op-batcher

Since none of the above changes affect L1 contract implementations, this maintenance upgrade will also not need a new OPCM beyond the one for Upgrade 14.

### **Conclusion**

This proposal outlines the features to be introduced with the Isthmus hard fork. These are key to maintaining parity with L1 and provide the best experience to users and developers of the Superchain that we can. We look forward to your support in implementing these features with your positive votes.

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_[View the full topic](https://gov.optimism.io/t/upgrade-proposal-15-isthmus-hard-fork/9804)._