Optimism activates the Isthmus hardfork across OP Mainnet and Base

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.