# Optimism activates the Isthmus hardfork across OP Mainnet and Base

> The watched chains became live on the Isthmus release, adding Pectra-derived functionality including EIP-7702 account delegation and blob-scaling changes.

- URL: https://riadefi.com/on-chain/2025-04-25-optimism-superchain-upgrade-15a-isthmus-prestate-blob-fix/
- Type: Upgrade or migration
- Stage: Executed
- Evidence: confirmed
- Materiality: material
- Event date: 2025-05-09
- Version: 2, published 2026-08-22 (first published 2026-08-22)
- Advisor-relevant: no
- Affects: Optimism canonical bridge (protocol); Base canonical bridge (protocol)

## What happened

OP Labs reported successful activation of Isthmus across the Superchain, including OP Mainnet and Base.

## What changed

The watched chains became live on the Isthmus release, adding Pectra-derived functionality including EIP-7702 account delegation and blob-scaling changes.

## What did not change

The release did not establish that either bridge became lower risk and reported no bridge-custody, pause-authority, withdrawal-owner, or governance-role change.

## Confirmed

- OP Labs dated activation to May 9, 2025.
- Base and OP Mainnet were expressly included.
- The release identified EIP-7702 functionality and increased blob capacity.

## Still open

- Independent verification of the final upgrade payloads and dispute-game prestates.
- Unexpected withdrawal-proof or fault-dispute behavior.
- Operator completion of required version migrations.

## What it means for an advisor

- Supersede the proposal-stage interpretation in both bridge diligence files.
- Verify deployed implementations, dispute-game configuration, withdrawal proofs, and operator-version coverage.

## Previous interpretation

Upgrade Proposal 15A was previously recorded as proposed and not operative.

## Sources

1. [Optimism Brings Ethereum’s Pectra Upgrade to the Superchain](https://optimism.io/blog/optimism-brings-ethereum-s-pectra-upgrade-to-the-superchain) · Optimism / OP Labs · 2025-05-09


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Published by Ketju Research on RIADeFi (https://riadefi.com). Educational research for financial professionals; not investment, legal, tax, or compliance advice.