🚨 Important Notice: Temporary Issue with Mailbox Backwards Compatibility During Protocol Upgrade v26

[uF4No]

As part of the ongoing protocol upgrade to v26 (ZIP-6 proposal), we have identified an issue affecting backwards compatibility with the legacy Mailbox contract interface.

Issue Overview

• Previously, L1 → L2 transactions were handled by the Mailbox contract (requestL2Transaction function).
• With protocol v24, the BridgeHub contract replaced Mailbox, maintaining a backwards-compatible interface.
• In protocol v26, the upgrade process is being carried out in two steps:
  1. (In progress) Updates applied to ChainTypeManager, initiating the transition of ZK chains to the new version.
  2. (Upcoming) Once ZK chains have upgraded, the L1 bridge upgrade will be finalized.
• Issue Identified: During this transition period, while both bridges and L2s are in different upgrade phases, the backwards compatibility of BridgeHub with the Mailbox interface is not functioning as expected.

Recommended Action

Until v26 is fully executed (~1.5–2 weeks), we recommend that developers migrate to the BridgeHub contract for L2 transactions:

• Use requestL2TransactionDirect or requestL2TransactionTwoBridges on BridgeHub contract instead of Mailbox.
• Once the v26 upgrade is complete, backwards compatibility with the Mailbox interface will be restored.
• Since Mailbox is a legacy contract, it strongly recommended to transition to the BridgeHub interface to avoid potential deprecation in the future.

BridgeHub Contract Addresses

• Mainnet: 0x303a465B659cBB0ab36eE643eA362c509EEb5213
• Testnet: 0x35a54c8c757806eb6820629bc82d90e056394c92

We appreciate your patience during this upgrade process. More information about this upgrade can be found in the ZIP-6 Protocol Development proposal, including the upgrade process.

For any questions or issues, please reply below or create a new GH Discussion thread.